Well, there was an M sport package for the 540, not sure if it came on the wagons though. It consisted of M bumpers, 3.15 diff (not sure if LSD or not), M5 wheels, and M steering wheel. There may have been a few other cosmetic items. You can check for a 3.15 by simply checking rpms at 3000. Should be 88 mph (+/- a couple of BMW speedo accuracy). Stock diff a 2.81?This is a new one on me. An e39 540 wagon with the "M5 Package." BMW 5 Series M5 | eBay
Now, it has the stock 540 grills, sits higher than my 540 sport wagon, has an automatic and has an m62 engine, so I am wondering what exactly comes with the M5 package? The style 66 wheels came with the sport package on my 540i6 sedan, but if this car had a sport package presumably it would not have a 2" fender gap in the front.
I'd be interested to see the dual exhaust setup, as my 540 wagon has a spare tire and no room for a muffler between the tire well and battery on the passenger side.
The car in the ad does not have dual exhausts. It may have some splitter in the back. The spare tire well would be in the way of true dual exhausts. Get a picture from the underside of the car and that should clear up any issue about the exhaust.
Otherwise, it seems fairly represented (other than "ignore the stains" which have been removed?) with the 4.4L motor and auto tranny. So probably a seller really not quite understanding what the car is. But someone spent some time and effort to the get the side and rear badges to make it look like a true M5.
Regards,
Jerry