In all of my 30+ years in the trade, I never once did a leak down test... and quite frankly never hear of such a test until many years after I retired, and that was via the Internet.
I was more interested in the compression test of which the numbers you listed (121, 129, 121, 128) are within the ballpark for a 1984 140 hp Evinrude/Johnson, plus the readings are only 8 psi apart.
The engines that were subject to piston ring breaking were what was called "High Ring Pistons" whereas the top piston ring had but a few thousands between the top edge of the ring and the top edge of the piston.... this existed many years back in time from the manufacture of the 1984 models. Your engine has approximately 1/8" of piston between the top of the piston ring and the top of the piston.
Compression is all important, and in my opinion, at the present time, the compression readings of that engine are fine..... and the leak-down test is pure bullshit! As with all engines, there is bound to come a time when some failure will take place, however I see no indication of it in what you've had to say.
