Hey-
I had the same problem with my DT300i oil change. Plastic 17mm bolt stripped and would not come off. Nothing worked at all.
Then I went to Harbor Freight and purchased the 9 piece metric extractor socket set which has a 17MM included, cost around $20.00...great sockets, removed stripped plastic bolt in 2 seconds when nothing else worked. Purchased new plastic 17MM bolt from parts monster for $35.00 with shipping - what a rip off....
http://www.harborfreight.com/9-pc-38-in-drive-metric-bolt-extractor-socket-set-67894.html