I guess this thread has gone cold and I need to fall back on a visit to the dealer and lots of expense.

Given the satisfactory level of fluid in the reservoir, leakage (even though there is some seepage) is likely not the culprit. Checking other cylinders for seepage does not seem to be a promising diagnostic path.

My (admittedly novice) opinion for the most likely suspect is the hydraulic pump, since the faltering performance of the top-up or top-down operation seems irrespective of which phase the top is in or which hydraulic cylinders are being used.

Any further thoughts?