Jetta 98 keyless entry problem

I have a ’98 VW Jetta. I purchased a new replacement key fob for the keyless entry because the original two that came with my car no longer work (the buttons disinigrated). I could still use my key in the door to unlock and lock my doors with the alarm working – just not with the key fob. I had even replaced the batteries with brand new ones. I took it into the service department for them to program the new key fob and they were not able to do so. They checked the signal from the key fob and said it was strong. I then had to pay them $82.00 to for a “visual” diagnostic test and to get it working again. When I got the car back the keyless entry would work sporadically; once every 8th time or so. I took it back to have them look at and they said I would need a new alarm modulator for $297.00 and now the alarm does not work at all. My car just locks and unlocks – no alarm, no red light on the door.

Where is this alarm module at so I can “look” at it? Can I replace it myself?

Does anyone have a suggestion as to how I can fix this? Please help!