Assuming the valve body is in good enough shape, swap in a TransGo valve when you do a fluid and filter swap and you should be good to go. It's about $50.
TransGo-5HP-24-PR-Pressure-Regulator-Valve-Repair-Kit-ZF-5HP24-A-BMW-Audi-Jaguar
The stock valve eventually allows pressure to spike and blow out the lip of the "A" basket. Stronger baskets are available, but that is the symptom, not the problem. TransGo valve should eliminate excessive pressure that causes the problem in the first place. If your valve body is worn excessively, that can also be swapped out, but I doubt it.
Also, if you park on a hill, come to a full stop, foot on brake, switch to NEUTRAL, apply parking brake. Lift foot off brake. If car rolls then the parking brake is not doing its job and you are resting the weight of the car against a tiny little pin inside the transmission while in PARK. This will make it hard to shift out of park. If the Parking brake works, then when parking on a hill, you should hold car with the brake, apply parking brake, then shift into PARK. That way the parking brake, NOT the transmission is holding the car.
For more info:
https://forums.quattroworld.com/a8/msgs/108743.phtml
Timing Belt? Hmm. Audi Engineers suggested 70k Miles or so, then a new law in CA said, all cars must go 100K before needing major repairs, and voila, with absolutely no part changes, the Audi service interval went to 105k miles. At this stage,if it hasn't been changed, change it, and the water pump and thermostat while you are in there. I'm a shadetree and have done bunches of them. Don't chep out on the water pump or the thermostat, especially with the thermostat go OEM. I think GRAF makes the waterpump and you can find those aftermarket. Expect to pay about $1500 at an independent shop.
Regards,
Brian C