Some years ago--I had a Nikonos cam and Ike strobes and various uw flashlights. I used the silicone grease that Nikon sold on cam, strobes, and lights. Some of the lights--Pelican I think, developed swollen orings and flooded, but the reason was unknown at the time. Quite some time after that, Ikelite said use only our grease on our orings as they might swell if some other silicone grease is used. I did as they suggested and had no problems. It all had to do with the composition of the orings and the materials used in the grease.
That said, I have stayed with Canon oring grease on my Canon housing and Olympus grease on the Oly housing. I use generic dive shop grease on all the lights. I've had no problems with swollen orings or floods in some years.
The equipment tech we use is very knowledgable and says he uses the generic stuff the dive shop sells on everything! The last Canon spec grease I bought was rather high at $11.42, but it will last for a couple of years----small price as far as I'm concerned...............Use a very small amount on the oring--a BB size glob may be too much--certainy use no more than that. A new oring every year or 2 is a good idea as well. You should be able to find all this on ebay.