I did the white spirit, then meths and then wipe/scrub with paper towel and that seemed to get it back to the original state.
When I re-attached I made the following changes:
Much less tape on the joint:
Single piece of gaffer tape on the back. Left this a little short of the cassette end to help clearance.
Single piece of tape on the front, I did not pull this tight, especially when wrapping over outer edge.
(I had about 3 layers front and back last time, maybe more at the edges due to overlap).
Made sure the zip tie attachments fell between spokes (last time they were resting against the spoke) and attached these to spokes on other side of the rim - to increase clearance.
Do the zip ties up very carefully, too tight and it causes another part of the cover to kick out (reducing clearance to the cassette).
When taping the rim I started away from the joint, and when overlapping (only a small amount) at the end deliberately went more over the rim than going back over the tape. This prevented 3 layers of tape over the joint/rim join…
The tape doesn’t stick to itself very well, avoid overlap where possible.
You don’t want the tape tight on the cover joint, especially when going over the edge. This puts stresses on the cover and therefore almost seems to cause the tape to pop off.
Less tape = more cassette clearance.
I’m still not 100% convinced by the electrical tape over the cover joint, but I’m quite confident with the gaffer tape on the other side. It seems fine around the cover/rim though.
What I might do differently if doing again:
I think I might use gaffer tape on the front of joint. Would look much less pretty and would be more of a faff to remove and clean up (I found it left a lot of residue). But it just seems to stick so much better.