Well today was a total ballache. Car up on the ramps and first problem is the fused bolts in the subframe. Under tray off and the subframe is looking like its on its way out.
I tip the engine flush into the engine. Run it for 20 mins and then go to drain the oil. It's the first time I've looked at this on the 159. Lo and behold I have a sump plug that is firmly stuck and rounded off.
New sump plug on order and now looking for a creative way to remove the old one. Hmphhhh!
Feel your pain, had exactly same problem with sump plug, its galvanic corrosion caused by a steel sump plug in an Alloy sump.
I tried several methods that you can try:
Soak some Plus Gas on the thread/plug but I know its not much to "wick" in, but worth doing before trying the following methods.
1) File sides of the plug to put a spanner on
2) Mole grips and may the force be with you!
3) Heat the ally sump around the nut with gas torch to expand the thread around the nut, then try 1) and 2)
4) Weld a nut on the plug.
I ended up welding a nut on the plug after trying combinations listed above.
There are suction devices that draw the oil from the dip stick tube if all else fails and I've used this one with good results too. They won't get every drop out from the lower part of the pan but better than nothing.