Camtech, www.zuiko.com will upgrade your OM-1 to use newer batteries (recalibrate the meter). John, who has deep experience, will also do a clean and lube.
I had him put in a beatty bright screen (with meter adjustment). My OM-1N is just as good now as when I got it in 1979 (has it been that long?). He also replaced my light seals.
Very good service. I have no connection with him other than being a satisfied customer.