What problems, if any, are to be expected when using 2N4037 metal can PNP transistors that were installed 40 years ago?
I can't divulge much about the design, but transistors are in a voltage regulator that was a spare that sat on the shelf for nearly 40 years, with short yearly tests. The other components (metallized mylar caps, carbon comp resistors, diodes) all seem to still hold their values within tolerance and work as expected. There are no electrolytic caps in the design.
Are there any common failure modes or pitfalls with these parts at this age and usage level?