Sounds like the vacumm lock mechanism is leaking or hanging up. (I think my 300D is doing that.) Might just want to spray a little lubricant on the moving parts and have someone operate the locks with the engine running to see if it frees it up. Do you have the CD manual? I had mine apart once a very long time ago but don't remember much. Seems to me you bought a mighty-vac, so you can use it to test the unlock vacumm can.