If it were the pump, it shouldn't have worked while off the ground, right?
I checked the fluid level & it needed topping off, but no biggie with the exception that the level indicator would get wiped clean by a foam like piece surrounding the dipstick every time. So I have to remove the top to estimate the level by eye.

Could it be as simple as the slight indentations the wheels have made while sitting are acting like blocks? (Sitting on particle board so as not to sink into the earth, but the boards are starting to give in to the weight.)

Would air in the line create a similar problem? (Thinking back at the line I noticed that has a pretty deep rub....)

Lots running round in my head....