I've got a 1996 chevrolet silverado Z71 its got the vortec 350. I am leaking oil from my oil gasket. Does anyone know a way to repair this without have to break everything down and put it back on?

 

Welcome to the forum

Oil gasket?
Oil pan gasket? where is it coming from front side rear?
The only way to correctly repair a leak is to removed the part, clean and removed the old gasket material and install new.
You may not be able to completely remove the pan from the truck but you may be able to lower it enough to remove old gasket and install a new one.

That said if its coming from the rear of the pan between the engine and transmission its possible its the rear main seal and that is a different story.

Thou as a "quick fix" try snugging up the pan bolts, it may just be an issue of the bolts working loose after time. Use a torque wrench to properly torque them don't just bear down on them and use the correct sequence.

 

I've heard taking oil pan off is quite a chore.. But then again, they told us that ATF change on Mazda 626 was $350, and we did it in the street corner in 30 minutes just with a jackstand...

Anyways, jackstand your trucks, get a strong hydraulic jack under the transmission, place wide board between jack and trannie, and you can jack engine up. another point to do so is main pully, but it's tricky to do, jack must sit on it really well.
if you losen engine and trannie mounts, you'll be able to jack powertrain up high enough to clear the oil pan removal.

 

Ditto on the previous comments. The best thing to do (if it is your oil pan) is to buy a new gasket. Make sure it seals right or else you'll be leaking all over the place. I have a pre-vortec 350 so the oil pan's real easy, but I don't know about the vortec's pan (if it's any different).