I have a kabota m6060 tractor 2016 My hydraulic pump out put is 1100 gpm,I need 1500 gym to use a rotro mower front loader.?

Does 3 point hitch operate, if yes then it's not the pump.

engine oil goes in the engine which will be at the dipstick hole or filler cap on the engine
anywhere else on the mower will be hydraulic oil

you didn't mention make or model; rear links are hydraulic?
If so did your "mechanic" put a high pressure gauge on the ram hose(s) and see what pressure there was? Problem could be in controller for link.

yes

There are air in the system need to bleed the system

first thing I would do is test the pump itself even if no wear is found you could have a GPM loss.
So you need to do a flow test on it to find otu how much the loss is and check it to the specs of that hydrolic pump first.

12 GPM will be plenty

Scott

Can you loosen the bracket that holds the hydraulic pump to get a little more room? Or can you get the pump drive shaft loose from the main pulley?

Sounds like you need more hydraulic oil - Or like you said the transmission screen (dirty).
Where it is ??