He sure did, and his website photography was great too. He knew how to present a premium product in a very flattering way. I've always been a bit surprised to see some top luthiers with dodgy photos or low resolution hosting on their websites. I love Alembic but their website photography is rubbish and seems to still be done with the same colourless digital camera they were using in 2005.
On the subject of the Bartolini electronics I suspected the whole thing would be proprietary. Indeed, I recall reading something from Mike from years ago where he said basses with electrical issues would have to be shipped back to him and any fault would likely necessitate complete replacement of the electronics. I know Mike liked to do a thorough job with his repairs and always seemed to go for the nuclear option of 'replace at any cost' over attempting a fix. That method does have it's benefits for customer satisfaction if not frugality. But it also led me to conclude that he either couldn't or wouldn't work on the electronics and to that end, I suspected they were entirely proprietary.
Now I gather in recent years that it has been harder and harder to speak directly to the pickup and preamp builders at Bartolini USA and that they do not have the capacity to do one-off custom jobs. I concluded then that it was likely that Mike probably bought sets of electronics in batches, ordered to his design, and that holding that stock was probably one of the drivers behind his insistence on complete replacement when a bass was sent in with an issue.
Mike's also been a 1-man show for a long time; diagnosing finicky electronics can be awfully time-consuming. 3 likely approaches:
1 visual / physical inspection for obvious damage like broken wires or solder joints
2 spray some tuner cleaner in the pots
3 rip it all out & install fresh
You can't really get into the preamp modules...