[Yamamaya42]

Since you are dealing with a temperature related issue on an older set, it may be advantageous to go with higher testing parameters when checking the resistors, especially when newer higher tol ones are much cheaper and very available, example, if the part is a 20%, reject and replace if it's out at 15% with a new 2% part, and if it's a 10%, reject and replace if it's like 7% or worse, or thereabouts.
Reason being, the more the old parts age, the more they will slowly drift out of tolerance and tend to be affected by temperature, the more newer parts placed, the less you will have to deal with later.