Browsing the web quickly revealed that DC100 tapes were scarce and unreliable, and it was widely recommended that the tape drive be modified to accept QIC tapes, which are not as ancient and a lot easier to procure. I placed an order for tapes and set about attempting both the necessary mods and the capstan repair.
The tape drive mod is described in detail here. It requires a change in one resistor to account for the slightly different magnetic properties of the tape. This was easy.
The mod also required the wheel to grow a little to account for the slightly different dimensions of the cartridge. This was hard. The last thing i wanted to do was to put the existing capstan in the hands of a tradesman because i feared for the rotary encoder.
Instead, i crafted a piece of plastic to glue to the top of the capstan. After a few tries, i got it to bond. I use the drive sparingly (i now have better alternatives), but the extension is still there many years later.
I worked through several versions of rubber replacement and eventually i had success with 6/9mm surgical rubber tubing.
Reliability is not great but, it is good enough to demonstrate operation. QIC tapes are tight in the drive slot, which makes them a little tricky to insert. I found that if i kept the front screws of the enclosure a little loose, it was easier to insert. Not great but acceptable. The alternative is probably a file.
Of course, once you have a tape drive and some viable tapes, there is the small matter of getting software on to the tapes.