How bad is it? The things are usually not too complex.
I have had to take a few Omega apart to fix the cams.
Sometimes a sideways knock in transporting it disassembled (or not) can cause a cam follower (that drives the dichroic filter in and out of the optical path) to hop off of the cam.
A gentle nudge and all comes back into line.
I had a Y that would not retract - the return spring had broken at the last turn where it attached to an anchor post. I formed a new bent loop and then swapped the fixed one in with the rarely used C one that was the same length so Y and M would end up having the same tension.
I had a Hansa head apart; poor light transmission was the reason. It turned out that the OEM assembler had not screwed the mirror box in place, just relied on double sided tape that had let go a few decades later. Installation of three missing machine screws scrounged from my 'little machine screw bin' put all in order. Then the spring that held the bulb in line with the optical path was missing. A bit of copper wire was bent and cinched to replicate that function, and it was fixed. I then was in a position to pass on another enlarger as part of my 'free darkroom kit' give away sideline.
I have another condensor Hansa that was just dirty; gentle wash of the glass and it was back in service. Then the PH212 bulb blew after a few minutes. I subtituted a spare Omega bulb, and adjusted the lamp base to get a uniform field of illumination happening again.
At Dave White's cottage I fed a little Durst condensor unit a 13W compact florescent in lieu of the usual photo lamp, since it is powered off of a solar panel and invertor, and every watt counts. The ouput was a bit too non uniform across 6x6. Since the new bulb ran very cool, I cut a panel of mostly translucent plastic out of the side of an empty milk jug and fit it into the lamp house light exit gate upstream of the condensors and all was well again.
Other fixes with diffusors can be the styrofoam lining which frequently lines the diffusion boxes falls out of place, or yellows.
The yellow symptom can often be remedied by either a small fragment from the home improvement store sytrofoam cut with a hot knife rig, or just turn the piece over if it is symmetrical and use the back side, for it is likely still white.
I wish I had the time to get to your place, but if you can get the head(s) out to my place one night or weekend with a power supply to light it up, we can take a peek at what ails them.
If it is in regards to Gallery 44's rigs, then maybe a discount on thier next workshop or group printing night of interest to me would be enough for me to get to these units where they are now.
Mike.
