Cant' get to the bolts (they are not exposed) for the nuts for the toilet seat. And, the bolts will not unscrew all the way. Can I cut them with a hack saw or will that prohibit the new bolts from screwing in? Thank you

I'm sorry to hear about the issue you're experiencing with your Coroma Opal II toilet seat. If you're unable to loosen the bolts that secure the seat to the toilet bowl, here are a few suggestions you can try:
1. Apply penetrating oil: Spray some penetrating oil, such as WD-40, onto the bolts and let it sit for a few minutes. This can help loosen the rust and corrosion and make it easier to remove the bolts.
2. Use a wrench or pliers: If the bolts are not budging, you can try using an adjustable wrench or pliers to grip the bolts and apply more torque while attempting to unscrew them. Make sure to hold the nut underneath the toilet bowl to prevent it from turning.
3. Apply heat: Heat can sometimes help break the bond caused by corrosion. You can use a hairdryer or a heat gun to warm up the bolts, which might make it easier to remove them. Be cautious not to overheat any plastic parts.
4. Cut the bolts: As a last resort, you may need to cut the bolts using a hacksaw or a reciprocating saw. Take care not to damage the toilet bowl while doing this.
If you're still having trouble, it might be best to contact a professional plumber for assistance. They have the tools and expertise to handle difficult situations like this without causing damage to your toilet.

There has to be either a nut and washer under the toilet, or if its reversed a bolt head with a washer under it holding it down. To remove it you can either use a hacksaw blade between the bowl and the bottom of the seat. Or use a dremel tool to slowly cut away the metal rod, etc., from the top. If using hacksaw put down some masking tape on the bowl so you don't scar up the enamel surfacr of the bowl. Work slowly and you will eventulaly cut through it.

Wrap a putty knife with a wash cloth, and push it between the toilet ceramic surface and the plastic hinge for the seat. Wedge it in there. Now try unscrewing the hinge screw. This provides back pressure against the hidden nut on the other side and may let you successfully remove the screw.

If the screws won't turn either way, they're probably "cross-threaded" or stripped. You'll have to unscrew them with force. I'd use a ratchet and socket on an extension (you might want to use a deep socket, since the bolts often extend an inch or two past the nut).

Once you get them off & can remove the seat, head to the hardware store or Home Depot & pick up a new set of bolts & nuts. They're very inexpensive. When installing them, make sure that the nuts screw onto the bolts with finger pressure alone, before taking a wrench or pliers to them.

If using force to unscrew them ends up damaging the toilet lid/seat assembly (this is the worst-case scenario), then you'll have to spring for a new toilet seat. The up-side of this is that new seat/lid assembly come with the screws and nuts, and - depending on what you want - can cost as little as $15 for an "economy" model, and up to $30-35 or so for a "deluxe" model.

I just had the same problem.I can not believe that kohler would design such a flaw. I have four of these toilets in my house,and it would be ridiculously expensive to replace, especially for a seat. To fix it I went to OSH and got some 1/4-20 T nuts, went home cut the bolts off the seat (multi master dremel) with metal cutting blade. With a screw driver tapped the bolt and the small area around the bolt down into the toilet area. Now you have just a porcelain hole. Clean area with solvent (lacquer thinner),get some gel type super glue from hobby shop and put it on inside and top edge of the hole on the toilet. Put some glue around the shaft and under side of the T nut and slip it into the hole.Then put a SMALL bead of glue around where the T nut makes contact with toilet and let it dry aprox 1/2 hour. Now you have a permanent fix.To prevent a problem getting the bolt out in the future,put some anti seize (auto part store) on the threads of the new bolts. Hope this helps.
Good luck
Max

Roberta3fan could be giving bad advice based on experience with other toilets. This does not seem to be an option for this toilet design. I am in a similar situation and it appears that the nut (and it is a metal bolt) is not what you would expect. Here is a picture of the anchor kit for this toilet seat: http://www.plumbingsupply.com/images/kohler-anchorkit-84999.jpg I am going to assume that the sleave that should be engaging the bolt is cross threaded and try to grab it with a pair of vice grips. I'll let you know if it works.

Here's what I did. Unscrew them as much as possible. Then I used a bolt cutter and hacksaw to cut away as much of the plastic seat holders as possible. I could then remove most of the seat, and get better access to the screws. I then raised the loose screws enough to cut them with a bolt cutter. Soft screws cut easily. The screw heads are now out. Now, tap down on the screw/anchor and it falls into the bowl. It will stay there. The remaining problem is that you need anchors to secure the new toilet seat. Kohler wants $50. I have a usable but loose seat. Never again-Kohler.
I strongly recommend using a boltcutter. A hacksaw will tear up the bowl.

your new seat will have bolts and nuts with it.

unthread the nut as far as possible, then tighten it one full turn. Cut off the top with a hacksaw or dremel grinder and re-try. The bolts are cheap. A small jewelers file may help. Look for the damaged thread and remove the burr.