Recently I realized McMaster Carr had X-Rings that are Viton and would fit our pushrod tubes. I ordered some test sets and they look GREAT!
I haven't used these on a car yet.
If anyone else wants to try some, here's the part numbers.
Viton Pushrod Tube Seals (small, X shape) 6540K152
Viton Pushrod Tube Seals (large, X shape) 6540K154