If the engtine is old and not got retainers ( for cam and primary chains) changed for long time they need to be replaced since the rubber wheels have hardened and will fall into small pieces. Cases must be apart for this (primary chain retainer).
I do not know the service limit but I can imagine 10 years when rubber hardens. When cases are apart there are other parts good to be replaced just for the cases are apart like all chains.
If tuning the engine, head and cyl off. Open the cases and replace all chains and retainers, seals, maybe all bearings, clutch...
Check if the gearbox sprocket dogs need undercut machining if they are worn. (my engine did not need it, now around 100.000km's,
Yes, it cost some....
