As fester said you shouldn't have any problem with the Penrite many others use it. Did you drop the pan and change the filter or just drain from the plug ??? When I do mine around 5lts comes out and goes back in.
I have mentioned it before but get a bit of flexi cable, like that wire curtain rod stuff, and dip the box, have it so it just touches the bottom of the pan if you have between 65 - 75mm all should be good, now thats cold on a flat surface.
Link:
http://www.ausjeepoffroad.com/forum/...d.php?t=106682
I ended up with a $10 job off ebay and it does the job but the proper way you need the temp and use the chart in the manual, a pain to do. Oil from an MB place is cheaper than dealer.