I have an 88 Cigarette Bullet with Mercruiser PowerShift. I shut one of engines off with the drive in gear at the end of last season. My plan was to use my hand operated vacuum pump to apply vacuum to the PowerShift unit and shift it back to neutral. I can't seem to get any vacuum built up in the Powershift unit by pumping the vacuum pump. Is the Power shift leaking internally or is there a flaw in my plan? Thanks!