preamp - price vs age

Call Cary and they will tel you that the failure rate on the SLP-98 is almost nil. The SLP-98 is over built, uses top notch parts, and the design parameters do not over tax the components. Also, the SLP-98 is very easy to upgrade and/or repair if needed due to the unit's point to point wiring.

I add a vote for a the newer unit preesuming less hassels.

For me it's worth. I usually tax the same amount if I pick up equipment to fix or to service (mainly studio gear and live sound)

Does`nt seem worth the risk and trouble to save only 200.00 dollars.Buy a later unit.

Finalize your work with resoldering all joints with fresh solder if you're savyy.

If it was working all these years and tubes replaced promptly, it shouldn't be an issue. Otherwise DC electrolytic caps might need to be checked/replaced for circuit safety reasons. Make sure to mark + - to avoid misconnecting.
For power supply and transformer I would recommend inspecting mounting tightness and replacing or adding soft washers or silicon between the chassis and mount.
Signal path caps less-likely need to be replaced.