The cell needs to stay sealed to enable the gas recombninant cycle. This takes patience but GOOP (only Goop) can be used to manufacture a rubber band between the case and the cap.
Micro tools, strong light and reading glasses if necessary.
Experiment first on cardboard
Dollop a spot onto cardboard. Leave a Hershey's Kisses tail on top.
It needs to dry overnight.
Then with a pair of vice grips or needle nose, yank of the Goop tail.
See how elastic it is. Almost unbelievable stretch and snap-back.
You need to make two spider silk threads from the cap to the case.
One on each side of the cap. 12 o'clock and 6 o'clock.
Dab a bit onto the cap. Then dab another bit at the base of the cap.
Then with a straightened paperclip, suck a thread either up or down and join it to the opposite dab. Straight up or straight down. Take your time. The thread has to be as, or thinner, than the paperclip
Do the other side.
Wait 24 hours.
Pull up on the cap. Elastic yes/no?
I've fixed a number of caps this way.
Fiddling with the Goop takes patience. Think hundred dollar bills...