I have been working on clearing violations with an abused motel 3 stop inground hydro. Working through all the rust, deteriorated sill, and rotten wood was a real challenge.

I have only been involved with this unit for the last month. Not part of the violations but instead a new issue that maintenance and the guests have been complaining about.
Only in the down direction at start there is a loud thud/ bang. Always happens at the 3rd going down and intermittently at the 2nd going down. Even in cartop inspection.

Speaking with maxton tech support about the valve. He quickly mentioned that the piston is most likely sticking and binding up do to lack of lubrication with old or burnt oil. He suggested lubricating the piston with maxglide or other additive. Mentioned to lift the wiper and poor onto the seal. if that stopped the thud then suggested to add a gallon to the power unit.

elmcanic sounds like as you mentioned. The piston is dry. What have you done in this situation??