David_sd:
I had mine repaired/recapped they are not difficult to work on and all the parts are available or have replacements. the amps come out easily and the diagrams are readily available, i have a set for the Mk1 if you need them i can scan them.
My thinking is most don't know what they are and hesitate, but in reality they are just amps and drivers nothing out of the ordinary or unobtainium as they say. also parts are still available from Studer i'm told. I also have the complete parts list.
I'd keep looking for reputable tech close by and take them to them and get them updated and repaired very worth while. if your going to have one looked at may as well get them to recap both of them while they are in there.
May i ask when you say one doesn't work what exactly is not working? could be something simple like a fuse, switch. one of the power connection on one of mine was loose and had a bad solder joint.