planning work out on car but can't remember what sealer...gasket maker...whatever i need to re-seal the cap on...anyone got recommendations or know what I'm looking for?

RTV, in a color of your choice because heat isn't really a factor back there.

Personally, I've never been a fan of RTV. I've never been good with it. Maybe I was using it back before I learned a lot of other things. Either way I prefer to use a gasket whenever possible. When I changed the oil in my diff I used a Felpro gasket. It was a rather plain and cheap looking gasket. It was less than $10. I figured that it was about the same cost as the RTV. The biggest thing with it not leaking in the future is correct and even torque. I'm glad I used the gasket because next time the job will be a snap because there is no old RTV to remove.

I just went to AutoZone and got a Fel Pro cover gasket. Otherwise black RTV should do the trick. There is no pressure or heat (well not alot of heat) so it doesn't take much to seal them up.

I like RTV. I've done about 4 Diff cover drops. I like that I don't have to fidget around to get the gasket lined up.

BUT, If you prefer a rigid gasket then get a Fel-Pro like BM96 suggested. They make great gaskets.

I use this Loctite product for gaskets:
http://www.amazon.com/Loctite-39158-Hi-T...=loctite+gasket
That is, when I can find it. When I can't find it I usually will tack it on there with a tiny bit of grease from the grease gun. I don't put anything on the silicone ones of course.

Victor Reinz RDS55341 from CarQuest. Cork over a metal frame.

The best gasket-in-a-can you'll ever find is Permatex "The Right Stuff". I sealed up my differential with that when I changed the fluid, and I used it to seal the oil filter adapter to engine block connection when I deleted my oil cooler. Neither area leaks in the slightest. Used it on other vehicles too, and not once has it EVER leaked.