I just purchased a 2008 Roadtrek Popular. All is well except I can not get the knob to open the propane tank. I just had it filled and the person filling it didn't want to mess with it. Of course I don't want to take a wrench to it. The propane place (a large U-Haul store) suggested I take it back to the dealer I bought it from; good idea except they are two states away. Any how, any suggestions on how to get this knob to turn safely? I was thinking about spraying it down with WD-40, but didn't want to go down that road with soliciting some advice. Thanks in advance.