[Premium-Rx] Racal RA-17L Overheating Problem

[William Watson]

Realizing that the RA-17L is not a "premium" receiver by today's standards (but still a pretty good radio!), I wanted to poll the group re a current problem with my RA-17L.
 
It has the top and bottom covers and is housed in the original Racal cabinet.  Works great until it cooks for a couple of hours and then performance suddenly drops way down.  I notice that by the time this occurs, the innards are very hot to the touch---including chassis and power transformer.
 
I am still in the process of isolating the problem.  So far, I have replaced the tubes plus an electrolyic capacitor.  
 
I was just wondering if any of you have any experience with those sets overheating?   
 
Of course, I could rig up a muffin fan, a la the Collins HF-2050 treatment and perhaps avaid the problem, but I would like to find out what is doing it.
 
I expect to eventually isolate the problem, likely to a heat-sensitive capacitor.  I did the customary refrigerant spraying on accessible parts on the bottom, but there are quite a few goodies packed away in the RF and other modules on top of the chassis that I have not yet subjected to that treatment.
 
I am currently in the process of taking a few key voltage measurements before and after failure occurs in hopes of finding a correlation.
 
Any thoughts would be welcome.
 
Joe
W5WBR