I own a 1999 A6 quatro with just over 266,000 miles on the odometer.

Approximately 6 weeks ago, as I was driving to work, my car overheated. I stopped and checked under the hood and the coolant reservoir was empty and steam was pouring out when I removed the cap. I had my car towed to a local mechanic and was told the Heater core hose was bad. Also, I was told this part could only be purchased at an Audi dealership. So one was ordered and installed the next day. When I picked up my A6 I asked the mechanic how long the new part would last? He said “for a lifetime”.

Well, this morning when I was pulling out my driveway the thermostat light came on indicating low fluid. I put the car in park and raised the hood. Sure enough, the reservoir was almost empty. Luckily, I had bought an extra bottle of anitifreeze and had it in my trunk. I added enough to get me up to the Min line and drove 22 miles to work. I checked the reservoir when I got to work and the fluid level was still at the Min mark.

I’m not sure what to do next: Go back to the mechanic who replaced the heater core hose, Or add stop leak to the radiator fluid Or have it looked at by my local VW dealership (they’ve done good work for me in the past) and are 50 miles closer than the nearest Audi dealership.

What do do you think my next step should be in fixing this leak? Other than the heater core hose, what are some possible causes of the leak?