That's a good question - not sure there's a definitive answer. Slight weeps are OK, I guess, but a sign that the shock it losing its pressure. If the entire shock body is covered in oil, it's time. But honestly - just based on the calendar, it's time. Replacing shocks once every 15-years is probably not excessive in anyone's book.My rear shocks are weeping slightly also - any advice on how to tell when it is time to replace? Thanks!