Mine did the same thing. Let me see if I can find the extras that I cut out of some left over plastic sheeting. I took the old one off, drilled a SMALL hole near the top, epoxied the replacement cover on (epoxy ONLY on the outside) and refilled it with glycerin from the drug store. It was very slow going and a bit on the messy side but it was over 8 months ago and it still looks good and no leaks. E-mail me your address and I'll send you one of the extra ones.

Bill Mattson, Certified Old Guy
Monty-less (right now)
Laura Mattson, Certifiable
Get in, sit down, BUCKLE UP, shut up and HANG ON!!!