I'd post this in Diesel Discussion or Tech Help, but frankly I'd feel too foolish, and I think it's best left to professionals at this point anyway.

Today I set out to do my first oil change on the 1985 300D I picked up from a forum member about 3 or 4 weeks ago. With oil, filter, tools, and the car up on ramps in the garage, I set out first to remove the top of the oil filter housing. The first danger sign was that I couldn't budge either bolt. I marinated them in WD-40 for a while to no avail, then asked my boyfriend to have a try. I wanted to know if they were really stuck, or if I was just 'being a girl'. He had to apply considerable effort, but he was able to dislodged both -- strike one for the girl

Next, remove the drain plug from the oil pan. The boyfriend, confident that nothing could possibly go wrong now, is on his way home, ten minutes into his drive when I call him: "So, how long should I have to turn this thing, anyway?"

When I first started ratcheting on the plug, it was tough -- very tough. So tough, in fact, that remembering with shame my earlier 'girl trouble' trying to dislodge the bolts for the oil filter housing, I resolved to brace myself and/or apply any leverage necessary to get that thing turning. The alternative, after all, was to wait until tomorrow, when the boyfriend would turn back up to rescue me, and I didn't want that.

I braced my feet against a tire and really hauled on the ratchet. Nothing happened. I tried again. It was verrry hard, but it moved a bit. I hauled on it some more, and slowly it started to give. Soon, I could ratchet one-handed. Five minutes later, I could still ratchet with one hand. Shouldn't something have happened by now? I expected the plug to fall out by now. Haynes didn't say anything about ratcheting until your arm fell off.

That's the point I called my boyfriend. "Do you see any threads?" he asked. Well... no. "If you turn it the other way, does it tighten up?" I tried it, and nothing changed. But after several seconds of ratcheting, it turned even more easily! I turned some more with renewed enthusiasm, but soon realized, I'm still not seeing any threads. At his suggestion, I tried loosening it by hand, but couldn't. There's no play in it at all, either, although more oil seems to be getting on my fingers at this point. It certainly can't be pulled straight out, and no matter how many times it's turned, it isn't coming out.

The conclusion seems obvious: I've singlehandedly managed to strip the threads on the drain plug, rendering my new Mercedes undrivable the first time I tried to do any maintenance on it.

I've gone inside for the night to ponder how to get the thing towed to someone who knows what they're doing well enough to fix my problem and maybe change the oil while they're at it. I'm also wondering how much the tow truck guy is going to laugh at me, and what this means for my future attempts at working on this car.

How bad a screw-up is this? Does this happen to everyone, or is this an indication of my blinding lack of aptitude? Has anyone else done anything this unforeseeably silly the first time out?