I am changing the lower unit gear oil in my 1964 Evinrude Sportwin 9.5 hp. Last year I couldn't find any nylon washers to replace the ones sealing the lower and upper screws in the lower unit, so I just put the old ones back in. They are pretty scratched up, and I'm worried they might leak. I couldn't find any that would work at the hardware store, so can anyone tell me where to find them? Can I just use an o-ring?