Jerry, don't you live in or near the Seattle area, so you could drop in on the company that makes the lift? Laura's original comment about the control box, and those about heat and the BCS techs not finding the issue, seem to imply the problem for many if not most owners is perhaps not in the mechanism, but either contacts or board solder points in the control box. Contacts arc and carbon up, and solder points on an integrated circuit board micro-crack from repeated heating and cooling; either one will result in the symptom of inconsistent operation - sometimes enough electric current can flow through and sometimes not depending on the completeness of contact.
Admittedly, yours seems to be more mechanical if its consistently operational from a partly down position, but it could also be contact positioning inside the controller or motor.
Joel