I hear ya. Skipp was referring to ChainDrive who didn't want to pop his side cover, after suspecting he's got bad juju inside. The side covers on these seal up readily, and stay that way if properly cleaned, torqued, etc. As far as original engines having a leak somewhere, we'd all be hard pressed to find a cheap, industrial gas or diesel engine that doesn't have a leak after 50 years.
I am just like you about leaks. I recently finished a Hodaka engine, and it ran great, tuned nice, didn't leak for two weeks, until much to my horror, I saw the tell tale drop of oil on the floor.
Not believing this engine would dare leak on me, I chalked it up to Carburetor over fill, or drain issues. After all, a 20:1 ratio of gas to oil in a hot, desert environment will look like an oil leak once the fuel evaporates in six hours. Nope, that wasn't it.
Pulled the side cover, re-faired, even applied some sealant over a new gasket. Nope. Two weeks later, there was just no denying it. The countershaft (chain sprocket side) oil seal was leaking about a drop every two days. Oil would collect in that side cover, then roll towards the front, then out to the frame to the next low point, and manifest a small puddle several inches from the offending seal.
Yesterday, I went back in, and found that the steel bushing that goes between the sprocket and the seal was worn after nearly 60 years of use, minus however long it sat out in the rain somewhere in Idaho. There was a groove worn right where the inner lip of that seal goes. When replacing the seals (and all of the bearings on that engine) I failed to replace a $4 bushing. Lesson learned. "Another" lesson learned I should say.
Skipp is right though, and I was thinking the same thing- there are indeed times when getting to something, or dealing with something requires less invasive action like adding sea foam, muffler grease, or in the case of my Hodaka, copious amounts of good grease garage soap sprayed on oily spots. But a Tecumseh side cover is a pretty simple fix, as long as the clutch isn't stuck. And as long as it doesn't have a bearing type of PTO where it has a seal that has to be destroyed to get to the snap ring to get the cover off in the first place.
In that case, it's still a pain in the butt, but not nearly as much of a pain in the butt as trashing the non-bearing journals of crank and rod. (Sounds like a smut magazine)