Elliot,

I had a similar problem with my 93 EV. You might want to check the 
receiver/dryer (a beer-canned sized cylinder) located in the right front 
wheel well. Attached to the r/d is a pressure relief valve which is in the 
line of fire for any debris comming off of the tire. My relief valve took 
one hit too many and began to leak.

You can check this valve (its about 1" long and facing into the tire) in the 
following ways: 1. is it covered with a thin film of oil? if it is...its 
leaking; 2. is there an oily spot beneath it on the ground? if so...its 
leaking; and 3. put some soapy water on the end...if it bubbles...its 
leaking.

In my case, the A/C shop that recharged the system swore up and down there 
were no leaks...until I showed them. If your valve is leaking, go to an A/C 
shop and get a replacement valve...VW doesn't sell the valve separately 
(although their parts catalogue shows one), you have to buy the whole 
receiver/dryer unit from them....$150+. I got the valve from the A/C shop 
for free.

Ric