i recently dealt with this on my ms290...replaced the pump/line/pickup then cleaned the vent and tank..ended up being worn worm gear threads and its brass bushing allowing it to slightly cock under load/rpm pulling the threads of the worm gear away from the oil pump. Looking at the old part next to the new part i couldent really see enough wear to think it was cooked, i condemned the new worm gears arm out of the package being it did not grip the worm gear firm enough and seemed bent away from the clutch drum enough to not ride in the top of the notch. These pumps are able to be disassembled by removing a roll pin to be repaired/cleaned.
Has anyone modified a pump by disassembling and removing more material from the notch/pump to gain more oil volume? these ms 290s seem to barely put out enough oil to run a 18-20" bar when functioning properly set at max output.