I'll bite. I am no oil expert, but I do know when you maintain a machine with care it will pay you back in service..... I always use conventional for a break in then switch over for small engines. Some of the cars ive had are a little different. I will note that the motorcycles run cooler and quieter with the synthetic that I've noticed over some years. They also tend to shift a little smoother and have less oil drag and clutch drag when cold. Ive read that syntetic oil will take a little higher heat before breakdown, but I have no hands on proof. For me especially in motorcycles with such low volumes it's a no brainer. This is just a list of motorcycles, but I've done some other for equipment and other things. My go to break in oil is rotella t 15 40 diesel oil. It has a high zinc content and no additives that will fubar clutch function. I also have a cummins that runs this and Ive been happy with it there too. NEVER use a synthetic with friction modifiers that is not for moto use in a bike or you will be sorry. Your clutch will work like crap.
honda crb600 f2 '91 (sold)
syntetic honda 10-40 (gold bottle) (3K changes)
30k miles before I sold it (2012)
didn't consume oil that I could ever tell and didn't leak a drop anywhere
original owner broke in meticulously per the manual
ducati monster m800s
synthetic motul 15-50 (3K changes)
doesnt burn oil. slight weep around starter on bottom of engine. Its on the fix it list, but you have to pull stator cover to have access.
dont know the break in
1982 honda silver wing GL500
synthetic castrol 4t 10-40 (moto specific oil) (3K changes)
no oil consumption or leaks
I wasn't alive for the break in of this bike!
GY6 based scooter (built to the hilt)
synthetic castrol 4t 10-40 (1K changes)
slight case leak (I suspect more due to shitty chinese parts)
gentle break in with conventional then swapped to syn.
castrol syn 4t 10-40 (1k changes)
14k on bottom end 3k on top end
no leaks or measurable consumption
ridden easy on conventional then swapped over