BigJohn

Can i just use the old gasket on the plug

CTB

I have re-used old oil plug gaskets before. Just make sure it isn't all bent up and out of shape. After you fill it with oil check to make sure it isn't leaking. Next time you are at the parts store, pick up a bunch of extra gaskets so you don't have to keep re-using them.

MTL_4runner

I have reused them too although you are not supposed to.
Just be very careful that there are no leaks after the change.
Take another peek in a day just to be doubly sure.

jx94148

I re-used one last year on the rear diff. It leaked very slowly all year and there would be drops of lube on the tailgate and back glass after highway driving. I changed it yesterday and it was a pint low. I got 4 new gaskets to do both diffs and tranny/transfer. Tranny and transfer take a different gaskes according to the Dealer parts counter. At first thay wanted over $8 for the 4. I mentioned TLCA and they came down to $4.13.

I think one cent worth of black RTV sealant would work just as well as that $2.25 gasket. I just felt like visiting the dealer for once. Maybe next year i'll see if NAPA has anything that will work.

I won't try to re-use them again for drains. For fill plugs, I don't have a problem with re-using them a couple of times.

MTL_4runner

You need to make sure the gasket goes back on the way it came off or it can leak....the diffs are tough because you really need to crank those fill plugs on there.....esp the drain one.

The diffs don't really have much fluid so be extra careful there are no leaks.

I don't suggest using any RTV because it can enter the interior of what you are trying to seal and possibly fill passages which should remain open. If you don't want to reuse the old one then buy a new gasket.