Back to tech: TK50 restoration and thoughts

Ok, so to get back to technology I have been working on fixing the TK50's I have here along with attempting to look at some old tapes from Bob's basement. It's been interesting. So far one of the units works well with one of my tapes (stored indoors for about 20 or so years) after a good cleaning with 95% isopropyl alcohol. From RT11 I was able to initialize the tape, write 40mb of .DSK image files, and consistently read the files back (to a VM: memory drive) and diff/bin them to make sure they are the same. Good. First test: A second TK50 drive I had banging around. This one will read the tape, but fail about half way through. May still be a bit dirty, will clean and check. Second test: Checking some of the tapes from Bob's basement. In addition to getting the PERQ tapes out of there I had a few TK50 tapes mixed in, most with degaussed stickers on them from long ago. These tapes appear to have been Vax 8650 load tapes of some sort, no idea if there is any value to the data but one was labelled Micro-pdp11 diagnostics and since I know those are backed up I started with that one. It loads, but fails with a DUP IO output error. It also messes up the tape head so I have to clean it after testing. Most of the dirt is at the bottom of the head. After cleaning the drive can load and read the "control" tape which has all of those image files on it, so it doesn't damage the drive. Still I see why taking the cage top off the TK50 is a good idea. :-) Took the cartridge apart and here is what I see: https://i.imgur.com/xHhiBAW.jpg This is... not good. Dirt or something on the bottom of the tape. Now these did spend the last 20 years in a pretty dank basement with an oil fired house heater so there is probably that. Still I used a Q tip on the tape with isopropyl alcohol and it came up dirty inside the cart and out: https://i.imgur.com/TB91gGx.jpg Also odd that the tape is wrapped in two different "levels" on the spindle. Maybe that's normal. So a question: Can one clean tape with isopropyl alcohol? In theory if I could get the controller to slowly run the tape onto the take-up real to the EOT marker I could soak some cotton swabs and use them to clean the tape before it hits the heads (to minimize head wear). Or I could just chuck these tapes and see how a couple I am buying from Ebay hold up. This is mostly an academic exercise: It gives me something to do. But I am wondering if the tapes were crudded by the environment or if this is just natural tape degradation. I do have one final tape that was in a closed tape holder so it might be better (it's clean on the outside). Will see.... C