How much paint should I strip?

[tomtheelder2020]

My 70 y.o. house has multiple coats of paint - not sure how many. In Sacramento valley so hot summers but temps rarely below freezing. Some of my steel casement windows are already hard to close all the way because of paint build-up. I plan to strip* at least the surfaces that contact when the window shuts (followed by oil-based primer). I would prefer to do just the necessary surfaces - i.e. just narrow strips. I am concerned that where new primer extends over onto old latex the paint might fail. I am hoping you all will convince me that the top coat will bind it all together and I am worrying unnecessarily. What say you?

 

[oldognewtrick]

Is suggest going to a paint store, PPG Porter Paint, Sherwin-Williams, and not the big box stores and talk to their paint rep. They will direct you to a product that will perform.