I recently purchased Leitz Focomat V35 with color module and I intend to use the color module for BW multigrade papers. A friend of mine recommended not to do so, because this is more than 20 years old and the filter color must have been faded away. Of course I don't want to start to use new equipment from wrong standard setting.
However, I don't want to attach external filter (this enlarger has no grade filter attachment holder below the lens and I have to modify it to do so) and want to use color module. If the color module filters are faded, is it possible to replace with new filters and where can I get them? I never disassembled the module and don't know how it is constructed.
Filters do degrade with time and exposure to light. That is one reason why more modern enlargers used dichroic filters, as they are less subject to deterioration.
You can test them if you have a color densitometer. The yellow filter for 0.1 density should measure about 0.1 to blue light and etc. If they deviate more than 0.05, either way, they are probably starting to go, but you could still use them if they give reasonable / repeatable results.
They won't fade away because they are dichroïtic but you can check that with a borrowed color analyser.
The only interesting upgrade for the V35 you can do is buy a split grade (tm) module from Heiland which gives you a quick measurement and automatic control for exposure time and gradation in 1/10 steps.
Another important thing is the right bulb: Philips 13139 75Watt.
The Focomat V35 is in fact the best 35mm enlarger you can buy.