Just picked up another Volvo 240 and getting it road worthy since maintenance was neglected. It’s very high mileage with an unknown amount but definitely north of 300k. My experience on other vehicles have been that if a seal is high miles and still not leaking, I’m probably better off leaving it since my skill level will seldom result in a similar sealing if I try to replace it with a new one. I have had many new seals leak where an old one never did. Take a look at these pics and let me know what you think.

 

I have always replaced those seals as a part of my timing belt change since it is all apart anyway. I have never had any problem with them leaking as there really isn't any significant pressure behind them.

 

definately replace. Seals cost what $10 and since you already have the disassembly work done, I'd replace anything that is accessible.