I have about 10 years on a rebuilt 235 without the hardened steel valve seats. I am not worrying about it.
A funny story however, an old timer very knowledgeable in car restoration and very mechanical, told me to add one cup of ATF to my gas tank at each fill up. Being young and naive (okay I lied about the young)I thought if one cup would work the whole quart would be better. No! It smoked and popped and stunk and I never used that stuff again.
