I'm betting it is not an oil problem. I had the same problem over a year ago when my 2010q was brand new. Lots of people apparently experienced the same thing. I contacted Juki USA in Florida and verified my serial number and purchase date and they sent a new walking foot covered under warranty. It seems there was a batch of walking feet that were faulty and they had replaced many. Give them a call and I'm sure they will rectify the problem.
Cheers!
Tamme