1992 GMC Sierra Transmission leak

I have a 1992 GMC Sierra and the transmission is leaking a lot. I bought a bottle of Valvoline Max Life Stop Leak. Do I just pour it in or do I need to have the truck running, etc? I know nothing about transmissions, which should be obvious by my question. I also seldom use the truck, so it maybe gets about 500 miles a year on it, but I want to keep it.

Before using the stop leak you should find out where it is leaking. It may just need a pan gasket or rear seal those are both relatively inexpensive to replace and then the problem will actually be fixed not just patched up.

Well, its leaking underneath (naturally) just behind the cab of the truck. I looked underneath, but can't tell exactly where it is coming from, but there is a good amount of transmission fluid there on the carport concrete.

Hi Judy,

I would suggest NOT to mess up your transmission keep it clean with out the stop leak. If the leakage is under the cab, then you have to check the rear seal which is located around the drive shaft abouve the Transmission support.

I have a some GMC Sierra 1992 named TITANIC.