You must remove the drive shaft. But first block the wheels so truck don't roll.
Now take a screew driver a hammer and drive the seal out, you will loose some fluid but not much. If your good you can drive the new seal in with a hammer. If not they do make a seal driver that a parts store might rent you.
If you still have a leak and your sure its coming from the seal and not the yoke on the drive shaft. Then the bushing in the trans. behind the seal needs replaced, and that can be trickey. Don't forget to polish the yoke on the drive shaft were it slides into the trans. GOOD LUCK
The length of the 1991 Chevy 1500 transmission is 37 inches. The bell housing will account for approximately 5.5 inches.
You must remove the transmission are engine to replace the rear main seal.
That is a 1 piece seal. You will either have to pull the transmission out are the engine what ever you think is the easiest for you.The seal just drives in a housing over the back of the crankshaft.
The engine rear main seal can only be replaced with the engine or transmission out of the vehicle.
You will need to remove the transmission.
rear main seal is the gasket around the crank between the rear of the motor and the transmission. front and rear main seals are usual spots for oil leaks.
you have to pull the transmission out-- or the enging which either is easier
$500.00
You will have to pull the transmission out and remove the fly-wheel to inspect the rear main seal. It is a 1 piece round seal that slides over the rear of the crankshaft. If the rear main seal is leaking on that 2002, I would find that very odd.
remove transmission, remove rear main seal, install new rear main seal, install transmission.
Assuming we are talking about the rear oil seal on that transmission, if it has been replaced and it still leaks, check the condition of the universal joints in the driveshaft.
FIRST BLOCK THE REAR WHEELS SO IT DON'T ROLL WHEN YOU REMOVE THE DRIVESHAFT. Then take a screw driver and pop the rear seal out of the transmission tail shaft housing and then tap the new seal in with a hammer being carefull not to bend the seal.