That would be the crankshaft pulley.
Looking at the bottom side of the front of the engine at the crankshaft pulley, the CKP is at the 10 O'Clock position of the crankshaft pulley
If the cranks shaft pulley is seized, the whole engine is seized.
The most logical reason for the key or tip as you call it breaking off is probably a result of improper torque on the crankshaft pulley or the crankshaft pulley is out of balance.To prevent this I would highly suggest buying a new crankshaft pulley that will be balanced.To explain what happens over time the strain of adjusting the belts from the alternator and power steering and air condition pull the crankshaft pulley with varied tension and can cause the crank pulley to warp to a degree causing it to be unbalanced.While this may seem a bit strange the metal will be affected by this due to age,temperature,torque from the belts tensions pulley left and right.Best bet buy a new crankshaft pulley (note just look at the pulley while idling and see if is wobbling) this will tell you the pulley is warped or out of balance.Plain and simple!
No, but it can be replaced. I would recommend taking to a professional.
It's behind one of the camshaft pulleys. Why would a CRANKSHAFT position sensor be behind a CAMSHAFT pulley ??
No, a bad crankshaft sensor would cause the car not to start and run.
If your 94 GS300 has high mileage as mine does check the following. If you have plenty of coolant, the belt has proper tension, the water pump isn't leaking, the hoses aren't leaking, then you may want to check to see if the pulley on your engines crankshaft has separated. The harmonic balancer/ crankshaft pulley has been know to become defective on the GS300 after a ton of miles. My car reached the 350,000 miles mark before having trouble overheating. However, just looking at the belt and pulley spinning at normal idle with an untrained eye, you would not notice that for instance, the power steering pump pulley is rotating at a surprisingly low speed. Take a socket and long handle ratchet or breaker bar and place it over the nut in the center of the crankshaft pulley. Allow handle to wedge up next to something sturdy; next, manually try to rotate the belt a few turns to see if the the nut in the crankshaft pulley rotates or not. If it does not then you have located the problem. I hope this helps
if your fuel pressure is still good i would replace the crankshaft position sensor , it is located behind the crankshaft pulley, you will have to pull it with a puller.
there are no gaskets on a tension pulley ther is however a spring and yes it can cause the belt not to run smoothly
It's hard to prove fault in these cases but the timing belt change requires removing the crankshaft pulley. So the mechanic would have had to have at least seen its condition. More likely, he damaged the pulley in the process of replacing the timing belt. Maybe he used an impact wrench when he reinstalled it and the key wasn't aligned correctly?
If I remember right that would be the water pump so you probly need a new one.