That sounds like a good idea with engine flush, you then need to do an oil change, people use the incorrect oil, with these engines it's CRUCIAL they run on 5/30 otherwise it causes problems not least with sticking valves, clogged oil galleries and oil starvation, I always change all fluids on cars I buy anyway. They have solid lifters so they don't jam unlike hydraulic.

I would do the above as is simple and should be done anyway especially as you don't know history of car, then if still same move onto looking at the bigger things.

Martin