I replaced the belt about 5 months ago, now it keeps coming off, and is way too hard to get back on. It is as if the belt is too small by about 1/4". Any help or tricks to this?

What is the belt brand and number?

it is a duralast 940k6

That looks to be the right belt, are all of your pulleys good?

all the pulleys are good but, I've replaced a few of them. I've had the car for quite some time. I bought it with 41K and I now have 110K. Everytime; the belt has been hard to get on. Now, something is leaking (we can't tell what it is yet) so there is a slippery substance on the pulleys, that may be why it is coming off. We were able to get it off and on several times but now it'* as if the belt shrunk. How far (like in inches) should we be able to move that tensioner for slack? Maybe it is not moving as far as it should.

Smell the substance you might have broken a coolant elbow trying to get the belt on.

If you have any fluids on the belt it will come off. Like mentioned, check the coolant elbows.

ok, my back-yard mechanics have smelled it and (i think one even tasted it) but they don't know. the best guess is oil and no one has really looked very hard to try to find the source of the leak. we got the belt on by forceful actions, and and they cleaned it and the pulleys somewhat, it will probably come off again. I took it on a couple errands and so far so good. I've got a new question: How can I tell why the check engine light comes on, without an expensive diagnosis? the fre tester at the parts store can only test 1996 and newer.

Try this. https://www.gmforum.com/specifications-general-information-132/obd1-codes-retrieval-gm-1983-95-cars-trucks-%2A%2A-278820/

thank you, i printed that and it should prove helpful