This process starts with a compression test.----Post your actual values.----There have been issues with # 2 cylinder.-----And does the telltale hose come off the exhaust manifold ( side off the block ) , or moved to the top of the block?
I can not see or touch your motor.-----I believe the clutch dog is rubbing on either reverse or forward gear.-----Easy to adjust.----If that is not the issue then you need to investigate.
Many factory gaskets ( and some aftermarket ) have a coating on them.----Experienced mechanics know not to use sealer on these.----Saw a U-tube presenter put a VERY liberal coating of gasket sealer on carburetor gaskets.----Did not realize that he was plugging up the oil recirculation channel on...
An 87 model would carry a serial # starting with --B110054--- I think.----Internal reed valves direct air and fuel to the 3 crankcases.----Did that beginning in 1972.
Brother in law----Has lived in a remote town all his life.----Every time I went up there, he had a radio on day and night in his workshop.----Protecting the biplane he was working on I think.