I kinda have to disagree about these comments,,
With a SERIOUSLY used 149,, (not a garage queen, a weekly mowing machine,, etc,,) unless EVERY component is replaced,, and I mean EVERY component,, That tunnel cover has to come off at LEAST annually.
There is gonna be some issue with a machine of this age,,
Heck, I even tossed the four screws that held the cover on,, and switched to "sprung" cotter pins to hold the cover in place.
The cotter pins had the legs spread slightly, you would squeeze the legs, and insert the cotter pin, the head was big enough to not fall through.
Forward / reverse friction, the fan, relief valves, drive shaft components,,
THEN there was the accumulated dirt on the transmission that needs washed,,
pull the cover, PULL THE COVER,,,
PULL THE COVER!! 
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Pulling the cover off the 149, then pulling the cover off the 1872,, THAT was the reason I switched to a gear drive machine,,,