Flame sensor can only be cleaned so many times. Part from lennox is big $. Part from sinclairs is like $20.
Price is depending on who you know.....
It's a piece of metal.... No magic involved. Clean it as many times as you can. They will stop working eventually, but that is usually due to a crack in the porcelain, and the rod grounding out.
Keep it OEM. It will be a tad more $$, but it will fit, and work. What you save on the part gets burned up on retrofitting/modding a non-OEM part. That $20 part is going to cost you an extra hour in labour. And at $100ish/hour.....
Sounds like you got a retrofit board, Tom. If it is from the furnace manufacturer then it will be the "updated, better" part. Should work out nicely for you.
T