Aged components / service!?

Depends a lot. 

Worst case scenario in a pre-amp or other line level device is very different than the worst case scenario in an amp.

With a PRE or DAC, for instance, worst case scenario is usually replacing bad caps.  If your power supply caps on an amp fail, or the coupling caps near the output stages, etc. then you can get into a lot of expensive repairs, and if they used proprietary output transistors which are no longer made this could mean the end of the amp.

So for a 10-15 year pre with no signs of wear,degradation of sound or such it's OK (transistor), or should i stay away?

I have a CAT SL1 Signature preamp that I have been using every day for the past 28 years. Couple of years ago I measured the caps and all were to spec for micofarads and ESR.

So the answer is... it depends. But for the most part, preamps do not generate heat so the components spend their lives in their design 25C ambient air temperature, which makes them very relaxed and stress-free.

Before you buy an old preamp (or any other piece of equipment) one big concern is that some parts may no longer be manufactured. Toshiba had a lot of good transistors and current source jfets in the 80's and 90's that were retired in the early 2000's. So be careful poking around inside -- damage one of those semis and it cannot be replaced.

I agree with others. It depends. If we are talking about true high end equipment, then probably good. If not, no. Do you have something in mind?

I would buy Audio Reserch, Conrad Johnson, VAC, and some others without hesitation at that age.

Depends on the manufacturer. Companies like Dynaco and Hafler seem timeless.