Yo, long time since I've scored.
I've wanted a Tek 11801 since I passed on one two years ago. A friend told me about an 11801C in the SF area so I bid on it and won for $175. It presented on ebay as super clean and it was. What I've found in two of these now is that maybe due to the size of the frame, things have a tendency to work loose in them. It had an error we misread as easy but it turned out to be a time base issue that could have been a nightmare. I started reseating cables, cards, etc and when i got to one of the last ones, all of a sudden it booted clean. I reran the diagnostics a few times and it's been clean since. The same friend, a great guy, sent me a module from the one I passed on originally that he bought. I then found an SD-22 module for cheap, that worked well, so for cheap I'm up to 20gig. Sampling has limitations but it has value for the price I paid.
You might note from my approach above that I rebooted or ran diagnostics frequently during the cable reseating. I think it is important to do this for a couple of reasons. One is incase a new problem shows up you will note where you made the last adjustment or cable moved. 2nd, if you fix it, it is also valuable for the future as these problems might come back.
Jerry