Liberally coat the O-ring and the mating surface with Vaseline (pure petroleum jelly). That's right, the stuff you get at the local drugstore.
I first became aware of this in 1960 when I first hired into Continental Airlines. I was tasked with disassembling and cleaning and reassembling Hamilton hydraulic propellers. The domes are at least 16 inches in diameter and use a toroid type seal with a dimension of 0.5" x 0.75". The standard practice was to coat the inside of the dome with engine oil and reinstalled the piston. It took so much pressure to get the piston into the dome that we wound up using a very large Dake press.
On one such occasion a man from Pacific Aeromotive came to our facility to repair a damaged deicer boot on one of the blades. I was about to install the piston into the dome when he told me to wait a minute and he went to his truck came back with a large container of Vaseline. He told me to clean all the engine oil out of the dome and coat it with Vaseline. After I did this I was able to put the piston into the dome with one hand. He showed me that the engine oil would pull away from the surface where the Vaseline would not. Suddenly, I was a believer.
I later installed and ran Continental’s jet engine test stand. Our big job was to fix oil and fuel leaks that occurred during the build up and repair of these engines. Most of the leaks were caused by cutting of the O-rings when they were installed. This was quite common especially if a snap ring groove is in the bore of the particular item. In the 10+ years I ran the test stand my guys used Vaseline liberally and never cut and O-ring. We all had one pound cans in our roll-a-ways.
When Mira Slovak and I got our second demo Partenavia airplane from Italy we had a ferry company pick it up in Italy and deliver it to Florida. When Mira went to pick up the airplane the nose gear strut was flat, it has lost all of its oil. He got a mechanic in Florida to put new packings in the nose gear. As soon as we got it home Mira did a demo flight in Santa Monica where the nose gear blew all the oil out of it again. He got it back to Santa Paula and we pulled a nose gear apart. Sure enough the O-ring was cut or I should say chipped. I installed a new O-ring and slathered it up with Vaseline, started the lower cylinder back into the upper cylinder and put the jack handle under the tire applied a little pressure and it went right in. Mira was amazed at how easy it went in and said the guy in Florida had had to beat hell out of it to get it in there. To me, it was no surprise that the O-ring was chipped. Mira flew the airplane well over a year and no more problems. Of course I was no longer able to needle him about his hard landings.
I can go on giving you many instances where Vaseline works. Another place that it does wonders is on aircraft or automobiles with “spin on” oil filters. A very liberal coating of Vaseline on the sealing surface will practically ensure the filter can be removed easily, it's providing it is not over torqued, that is. Bottom line is “you have to try it to believe it”.
I will now step down from the pulpit!
DON VANCE