Bathtub faucet leaking a lot

call a plumber or get a key from a plumber supply shop

there is a manifold available from a good plumbers supplies shop where the taps are separate on the branch ( "T" bit where the spout is mounted) this allows the taps to be positioned on the branch to fit the holes in the tub, basin or wall
they are fitted using a ferrule (plastic or copper seals) and nuts and are tightened up when in position
If you do not have taps suitable for this branch then you will need to buy the taps as well
the branch will be around $20.00 and the taps around $30.00 each for normal screw inserts
ceramic inserts will cost around $60.00 each but will last a life time.
talk with the plumber supply shop for good advice.

Get a plumber 2 do this operation 4 U!!!!

being a plumber for 50 years I hate the new fittings . I still use plumbers mate = and boss white , with silicone under faucets .

With the detailed part number you have, I would just walk into stores like Home Depot or any plumbing store and they will give you the exact parts you need. They are not expensive and a lot of them are standard parts and come in kits.
Good luck.

you must use genuine kohler parts,if you got something from lowes or home depot that was some other brand they usually leak. also look for calcium build up inside the valve body,you can use 1500 grit wet sand paper to remove it just be carefull and dont sand too much,then apply water proof plumbers grease inside the valve body befor you install the new cartridge.

The gasket is installed on the outside of the tub. Use plumbers putty under the male end on the inside of the tub as it stays permanantly flexible and will not mildew like silicone caulking can. Do not silicone or use plumbers putty on the gasket. The gasket will seal nicely under pressure from the connections.

Yes the weight of someone in the tub plus the water can push the tub down far enough to cause the leak.
Unscrew the flange in the tub that holds the drain to the tub. Get some plumbers putty and make a bead to fit between the tub and flange.
Make sure the rubber gasket is clean ..use a bit of plumber's putty on this as well. Get an assistant to stand in the tub while you snug things up.
Snug it up tight.... replace if the threads are stripped as you said.
Plus if your house is less than a year old, I'd talk to the contractor/builder if possible about warranty work...most reputable builders will cover their work for the first year.

They do not all leak. The problem may be that your faucet is simply wearing out and is due to be replaced in total. Try putting some plumbers grease on the cartridge and the chamber.....not too much..........that may do the trick for u.

ouch sadly im sure it was pricy to have him out  so my suggestion would be to call him back and have him take off the price of what he charged you or have him fix it for no charge could be just need some plumbers putty around the faucet to stop a little water that may seep threw under the faucet good luck