Can you tell the part # for the plug
17-11-7-530-902 drain plug radiator - $4.40 from Tischer
I'm glad I replaced it, after 4 years of heat from the radiator, the plastic has to be affected, and I want to trust it'll last another 4 years. It located under two pieces of cladding, so there's no easy way to check on leaks from there.
I used low-pressure compressed air (5 - 15 lbs) to blow out the coolant (I duct taped a valve from my compressor into the reservoir fill opening, keeping the bleed value closed), and got quite a bit more out, but even with that, when I unfastened the hose off the pump, coolant drained from there (wear goggles or safety glasses, coolant splashes against the sway bar.) I let some fresh coolant drain through before I buttoned up the drain with a new drain plug to flush the bottom of the radiator.
I ran the pump routine 3 times (since I used compressed air, I wanted to make sure I got all the air out, and not risk damaging the head), but after the 2nd time I did not need to add coolant, so 2 is the magic number. After a week, I added about a cup of coolant.
All in all, pretty easy, except for pulling the hose off the pump, but that is worth it for the amount of coolant you get out from there. The Bentley manual also says to do this.