40hp trim pump bleeding

I have a 1986 40hp ETLK with power trim and tried to bleed the system since it needs a little help getting started moving lately. The S.S hex head "purge" screw won't budge. Any ideas? Also, what is the correct size allen/hex?

Mark

[boats.net]

To bleed air out of system, loosen the manual release screw on side of bracket. Lift motor to full tilt by hand, fill with fluid and then let motor trim down under it's own wieght. Repeat about three times keeping fluid topped off when in the up position. Tighten manual release screw.

Thanks, Yes I know the procedure. Here is the question/problem again.

The S.S hex head "purge" screw won't budge. Any ideas? Also, what is the correct size allen/hex?

[boats.net]

Probably 5mm but not sure, you shouldn't have to remove any screws to bleed air out.

Isn't the 5mm hex the manual release "Purge" screw? Thats what is shows in my manual and the stated procedure for the type "B" trim pump.

Thanks,
Mark

[boats.net]

The manual release screw is number 9 in this diagram, Yamaha Outboard Parts 1985 40ETLK POWER TRIM & TILT ASSEMBLY Diagram
Can be seen through hole in transom bracket to loosen.