Permatex Ultra Black Silicone Cap Mod to Prevent Hardening
 

I really like Permatex Ultra Black Silicone. I use it for many things on the Supra especially where sealing oil leakage is concerned. I've used it on valve cover gaskets, oil pans, oil hoses, transmission case sections, differential cover. It's as good or better than that orange FIPG Toyota sealant. The only thing that's trouble is once you open the tube, it tends to harden under the cap into the tube. Every time you go to get some you have to dig a hole through the hardened silicone. I tried things like screwing the cap down over Saran wrap and keeping it in a zip lock bag with not much success. Now, I think I've found an answer to this problem. Take a new or used 7M fuel injector O-ring that seals the injector to the rail and use it as a gasket in the cap of the Ultra Black. See photo. I did it a week ago and used some today with absolutely no hardening found. I recommend not cranking it down because the caps tend to split in past experience without an O-ring. Tighten the cap down enough to snug it. Another thing that also may help is to put a little bit of silicone grease on the threads of the tube to discourage air infiltration.

Here's an update: After many weeks I went to get some out of the tube and its working great. I did notice that the O-ring became glued to the top of the tube but that's ok. Just try and keep it neat after you take some out.