There's a LOT of debate about this actually. I don't remember 25mm actually fitting on my 1990 740's drain plug... and I've known other's who have had this problem. Could be something as simple as tolerances in the manufacture of a wrench. I've since always used 1" box wrenches on red block Volvo drain plugs. Bentley actually specifies 1". Weird, since every other fastener on the car is definitely metric.

Go to Sears, get a 6-point 1" Craftsman combo wrench. Big and fun just to hold in your hand. Use the box end. If there are worries about rounding off the plug when loosening, you're probably over tightening the thing to begin with. If you use a copper washer, there's no need to wail on the thing when you tighten it up.

Don't use an open or adjustable anything on this... and while I own a couple of big adjustable wrenches, my take is that they don't belong in an automotive toolbox.

-Ryan
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Athens, Ohio
1990 245 DL 133k M47, Cibié E-codes, Now with working wipers!
1991 745 GL 290k (Girlfriend-mobile)
Buckeye Volvo Club