If your hyd pump failed and you had debris in the hyd system, a good flushing and filter/strainer change is the first step.
I would then install a gate valve between the hyd CV and the mast, raise the mast up 24" and close the gate valve. If the forks continue to drift down, you have an issue in the mast lift cylinders or valves.
If the forks don't drift, but they drift once you open the gate valve, check your hyd CV, (poppets sticking, etc).