Remote key fob 986 - any fix??

[cuz3003]

I seem to have tried all of the fixes on the net but recently one of my keys stopped working. I changed the battery and still no good so just switched to the other key and all was fine.
Fast forward a couple of months and the other key now doesnt work i.e. I can manually lock\unlock the car but not with the fob. Changed the battery and no joy...
Any known fixes other than the usual resync attempts which havent worked?
Is it the key(s) or the alarm unit in the car.
Car is a 2000 S with no water under passenger seat.....
TIA

[SoliD]

How fast is the light flashing with the new battery? If it is very slow this is the same problem I had with mine and I needed a new keyfob.

[cuz3003]

It flashes very quickly with the new battery. Trying to work out of it is the key or the alarm unit.