I have a obsolete but modern-ish Whirlpool water cooler. The white plastic ring the 5 gallon water bottle sits on is cracked, and chunks are coming off. Whirlpool doesn't stock parts for old model

If the plastic is cracked, you only need the frame and you can transfer your glass dome to it.

A lot of money for a plastic ring! I would fill the cracks with Super Glue Gel and fill the back with Liquid Metal Epoxy.
https://www.geapplianceparts.com/store/parts/spec/WH46X25524

The glass is obsolete!
https://www.partsimple.com/15011048-amg-n-8.html

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Maybe, but you provided no info on the make and model of car. So, do a google search. I suspect you will find the bottle and ring but not just the ring.

Most common cause would be a blown head gasket or (similar failure) - in which case the oil on top of the coolant would be brown-ish in color.

Or, less commonly, a failed transmission cooler (built in to the bottom of the radiator), in which case the oil on top of the coolant would be pink or red-ish in color.

More details offered in your question, such as year, make, model, and mileage could possibly yield a more comprehensive answer.

White smoke normally indicates a cracked head or bad head gasket on a water cooled engine. If it's going through a lot of oil, the exhaust is caked up with oil or you see black smoke, it will either be valve stem seals and/or worn rings/cylinder bores. Blue-ish smoke means the engine is running rich.

White coming out the tail pipes is coolant/water. Doesn't mean the head gasket is blown, but you'll wish it was. Could be a cracked head. They can crack inside the intake or exhaust port. This would still give you a good compression reading. If in the intake, you would have a misfire. Exhaust you wouldn't. As far as the blue goes. It is mostly white in color, with a hint of blue color. Loosing that much oil would be a major leak or the rings are shot. Rings being shot, you would see that blueish tint in the smoke.

There are .26417 US gallons to 1 Liter
OR
0.2199 Imperial Gallons to 1 Liter

Sounds like either a blown motor (rings need replaced) or a bad head gasket or cracked head.
If the rings are bad your car would have felt like it was losing power because the engine will no longer have the same high compression that it's required to turn the wheels. You may have heard your engine knocking or seen a light blue colored smoke coming from your exhaust as a result of your engine burning up oil in the combustion chamber from the rings leaking.
If your head gasket is leaking or your head is cracked you'd likely find milky looking oil when you drain your oil from water/antifreeze being mixed in and noticed a white smoke coming from your exhaust that is actually water vapor coming through the exhaust.
If your car was running rough when you last shut it off try pulling all of your spark plugs and either cleaning them or replacing them all. A bad head gasket or bad rings can both foul spark plugs. A car will run rough with 1 or 2 fouled plugs, but once enough foul it will no longer run at all just sit and crank over. If changing the plugs get's it started for ya, check your tailpipe first for water, if nothing, change your oil. If no signs of water/antifreeze or milky colored oil then it's probably rings.

Water for what? Do you mean engine coolant? If so you top it off at the engine coolant surge tank under the hood, it is a plastic tank with green or red or yellow fluid in it (most common colors of modern coolants), use a 50/50 mixture of coolant and low alkaline water like drinking water from bottles about 90 cents a gallon at the local Safeway or Lucky super market..

Some of these vehicles have a false petcock. Pop off the lower hose over a catch pan, pour a gallon of water in the plastic Dexcool Coolant bottle and put the hose back on when it stops pouring out. Fill to the max line and run the car until both radiator hoses are hot (thermostat has opened). Replenish fluid to max line and cap the bottle. If you have electric fans make sure they come on and make sure your temp. gauge stays in the middle. It'll take longer on cooler days. You might have to get in the car and gas it to about 2000 rpms. Don't cap the bottle until the thermostat opens. If it vomits, change the thermostat and again make sure the electric fans kick on or the clutch fan speeds up at about 210 degrees.

may have hair line crack in coil,,or bad wire,,spay wire while running with a water missed spray bottle,,& see if u can make it misfire,,start at spark plug & work ur way up,if it starts to misfire when u get to the coil,,u will no with part to replace,,hope it helped,,