Mk4 vehicles had an aluminum oil pan. VW used cast aluminum oil pans on these cars to muffle engine noise. That's a good thing. The problem occurs when oil change techs overtighten the bolt, or try to install the plug with power tools.

It's important to understand that lube guys are not mechanics. They may be mechanically-minded, but they lack the training and experience to do most technical labor operations and the fact that drain plugs are frequently being stripped by them is evidence of that.

The dealership would sell you a new oil pan for hundred$. We can replace those threads with something even stronger than factory. Helicoil! Stainless threads that are permanent. It requires drilling a larger hole, using a special Helicoil tap to make new oversized threads, then drawing a coil of stainless wire into the new threads that create new, perfect threads that are harder than aluminum, harder than even the steel drain bolt.

Oh, I see you've been going to an oil change place!

Drilled oversize and tapping with Helicoil special tap. Perfect angle is required for washer to seal.

Oversized threads, ready for Helicoil to be drawn in.

Attention to detail is vital to this job. This is a machine operation, requiring the threads be cut at a perfect angle. If the angle is not perfect, the washer will not seal evenly on the flat shoulder around the threads. The threads do not seal the oil. The threads pull the bolt against the washer, making a perfect seal against the oil pan surface. Patience, attention and a steady hand are required to do this properly. This work is $100.00 when done in addition to an oil change. So it's oil change + $100.00.