first steps
I JUST did this on my MS250, which I understand is the same.
Before you go to the extent of removing the oil pump, check the tank and filter first, my tank had quite a bit of crud in it, clean and rinse.
Then blow out the vent on the side, then remove the handle to pull out the oil line, check, clean and refit the whole shebang. The manual says you need a new o ring for the plastic thingy, I had one slightly smaller, seems to be working fine.
Test for oiling.
If no joy then take off clutch and check worm gear. You need a special tool to extract the pump itself so I didn't go that far, but when I put it all back together if oiled just fine, better than it ever did straight out of the shop.
I'll email you the shop manual that 04Uta sent me, share the love...