Omega fob repairs are remarkably easy, I've had to do loads for various members.
For 2 button fobs, the only common fault is the battery holder becomes detached.
For 3 button fobs, the switches fail, and the same battery holder fault.
Switches are simple replacement. They are surface mount, but any fine soldering iron is good enough. Battery holders, the way I do it, remove holder, extend the (broken) leg(s) with stiff, fine wire - resister legs are my usual - and then solder back in. I also tend to use a dob of glue to add additional mechanical strength to it.
On 3 button ones, if the switches have been knackered for too long, the fob casing gets knackered from you pressing too hard. Replacement fob casings are available on egay for £2-3, but they are much harder than the GM ones.
If you have programming facilities, 3 button fobs are quite reasonable from dealer. About £25 + VAT was what I paid for last one a few years back.