Been through all of this and offered up my airplane to both Garmin (600) and Genesys (3100), along with all costs. They are not the least interested in the Skymaster. I get it, though. Have you looked at the average Mixer? In my travels across the country, I see 337s on various ramps, and almost all encounters are examples are spent airframes. Sure the pretty ones are in hangars and cared for, but I am willing to bet the majority are at their end. Not good. Remember that those of us represented here have a very unusual interest in an airplane that is a 43-year-old airplane at best.
I've been thinking the same as GAdams as of late; about all those 55 that have been traded in.
For me, right now, my 400A is still great. When I was last at APC, I bought a spare G-519-A Attitude Indicator and had APC calibrate it to my airplane. Sure enough, it failed earlier this year. I slipped it into the panel, and my autopilot never knew something had changed. I plan to schedule another visit to APC this year to ensure everything looks good.
My airplane is in the shop right now with everything out of it. An Aspen 2500 Evolution Pro system is being installed. I decided to stick with my two 430Ws as they went through the Garmin refurbishing two years ago. The AI does have to remain in the panel, but there is very little between the panel and the firewall now. The airplane is scheduled to be out of the shop in 20 days. The picture is back from mid-December.
The 400A needs the AI pitch and roll, but the Aspen system can handle all navigation inputs from there.
This is probably it for me; I'm 69 and will ride the airframe out from here. The simplest of parts could end an airplane. I'm constantly chasing components, it seems. Also, it is getting tough to find someone who can work on the airplane without paying to train them as they gain experience. Most shops I've contacted are not interested in the work.