OT & FOAK: Suction cups for cables

An odd one, I admit.

My SatNav has a TrafficMaster antenna which fixes to the inside of the
windscreen by means of two small (approx 23mm) clear plastic suction cups.
The problem is that one of them has developed a hole in the middle of it, so
no longer sticks to the screen. Just to make matters worse, the suction cups
have a circular hole drilled through the top that the cable passes through,
and the cable has a non-removable end cap, so I can't just thread on a new
one.

So, problem number 1. Halfords are claiming that it's "wear and tear mate",
despite being only 2 months old. Not too pleased about this, but never mind.
Noted for future reference.

Problem 2. I can't seem to find anywhere that will sell just spare rubber
suction cups! Maplin was by best hope, but no luck there.

Problem 3. If I *do* find said suction cup, it's going to have to be one
with a small cutout to clip the cable into place, as I can't thread it
through the hole.

I'm trying to contact Garmin to see if I can just blag a replacement antenna
(not hopeful!), but I was hoping the FOAK might be able to point me in the
direction of a supplier of these seemingly rare suction cups!

Can't you just smear a bit of clear non-hardening silicone over the
hole? Window frame or bathroom sealant should to the job.