The deformed part is the water moving around the sleeve. I can unscrew the cap, but not the top piece itself. Feels like it's been glued (pvc glue) to the PVC pipe below. My PB isn't responding, which is par for the course with him.I would ask you PB to come back and show you how the std 1.5" umbrella fits in the hole he installed.
Since it looks like it screws in, you could unscrew the sleeve, then dremmel out the inner piece. It also looks deformed too where it might be pushing into the center, thus blocking the pole - was this already used ?
I would go to a brick and mortar pool store and look at their umbrella receptacles and compare that to what you have.
I thought about this as a possible solution, but think the umbrella would be pretty unstable sitting higher up in the sleeve.I wonder if you can find a short piece of PVC that will act as an adapter... both fits the umbrella pole and the other more narrow end into the hole? Don't they have pieces of PVC in the plumbing section like this??