I have a mk1 dt125lc and having recently rebuilt the old engine,i am losing gearbox oil,fairly quickly.theres no obvious signs of it leaking externally so im presuming the oil is getting sucked into the crankcase (i would have thought it would run smoky but it doesnt seem to run too bad).i joined the cases with threebond 1104 on assembly.anyway-anyone with any suggestions as to a cure and how to go about it?

Pete

Strip it down and do it again.

Its either,

duff sealant

bad seals or fitted the wrong way round.

cracked case.

Any way you spin it the most sensible way to check is strip it back down as sods law says the last thing you check will be it.

how about pressure testing somehow by applying pressure to the vent hose?

the bond you applied is for mostly external sealing. more than likely you have a blown seal! if its losing oil and not externally id say you need to pull apart and have a look at your seals. i know it sux doing it all again, i once rebuilt my sons fk60 3 times to find where a left over part went only to have master 7 walk in the shed and identify it as a part off his skooter he had been working on and placed on my bench with all the engine part! aaargh!lol

Does the 125 LC have the little o ring on the crank under the primary drive gear collar like the 175?

That would do it.