First Do a proper leakdown test. It's got to pass to run. No need to disassemble except to drop pipe. I use a harbor freight four stroke leak down coupled to an air compressor that has an adjustable output gauge down to 5 psi and to 14 mm sparkplug hole with Piston at bottom dead center. A helper plugs the exhaust port with I find the fat fleshy part of her or his thumb and 7 psi is intraduced to the case. Yes I used the reeds block to close the intake. Now take a spray bottle with dilute johson and Johnson's baby shampoo and spray some typical culprits ( obviously not seals because u haven't disassembled down to seals but if it holds 7 psi with the gauge reading green ( intake of compressed gas to maintain 7 psi ) I hope !!! I think you are mostly good and can proceed without pulling magneto and variator seals. Another good thing is now u know also that the reeds close correctly. You don't know how they open. When I built the Athena motor that cheetachrome kindly ported the case I couldnt get that thing starting on carbon Reed but like a charm with the fiber ones.
So do yourself a favor and try this approach. It's systematic. There is also a opposite test that your can do to measure if there is a one way leak from outside in by adapting the test to a applied vacuum also with cheap vacume testers at the harbor freight types of places that if you do a good search on all forums all.dates with the right search term ( start with something like "leak down" ) and go from there. Good luck if you haven't found it yet.