I recently had a TS250/1 and a ETZ250 engines stripped side by side and looked at the differences in the gear boxes. The 3rd gear woes are well known and I have also heard of 5th over heating at sustained high speed. The only significant difference I could see was to what I call the oil drip tray.MZ had obliviously tried to increase the oil dripping on the cluster. I have heard that ETZs suffer more than TSs so it obliviously did not work.
I noticed a lot of casting remains which could restrict oil getting to the drip tray on the TS so I removed them. The oil is fed to the tray by being thrown up by the clutch / primary drive, I wondered if the oil could not replaced in the primary case fast enough to feed the drip tray at high revs which would explain the revier ETZ suffering more. I then checked the hole allowing oil into the primary case and found it was smaller on the ETZ .The ETZ was a parts donor for race TS engine so I used the ETZ drip tray and enlarged the hole for oil to get into the primary I don’t know if it has helped but the gearbox is performing perfectly after a season of racing and parading .We all know long it takes to fill a TS/1 or ETZ gear box due to the oil needing to fill the primary case so hopefully these mods will help. I hope this is helpful to others.