Natural rubber is affected by mineral oils. The self sealing tanks of spitfires etc had a natural latex rubber called Linatex in a layer around the fuel tank. If a leak occurred due to a bullet hole the latex expands and seals it.
htts://www.global.weir/newsroom/news-articles/five-unconventional-applications-where-linatex-rubber-stands-the-test-of-time/#:~:text=Famously%2C%20Linatex%20%C2%AE%20rubber%20was%20used%20to%20line,it%20prevented%20fuel%20leakages%20and%20the%20resulting%20fires.
The rubber beading on the mog will be a synthetic rubber that isn't affected by mineral oil.
