Looking for advice, i recently re-built engine (been ongoing for last couple of years) 90 % of parts were bought from TY Offroad.

when started engine after 3-4 mins it starts loosing oil from right hand side of cylinder (from head gasket area) 

when i re-built i checked both the head and barrel and both are dead flat. The only thing i noticed was that the new head gasket (copper) doesnt have room for the o ring on oil passage stud.

anyone else seen this or what was your fix?

reluctant to use sealant around oil feed

No experience with this, but can you modify the head gasket so you can use an o-ring?

My old Norton required annealing its copper head gasket to ensure a good seal. 

Good idea Konrad! I just wanted to add, in case you don’t know davy1 how it works.
Copper annealing works great to revive “work hardened” copper. This will allow you to reuse used copper washers over if you don’t have a new one handy. Work hardening happens when you, for example, tighten down your oil plug. The tightening squishes the copper washer to make a good seal but the squishing hardens the copper. That’s why they always say to replace the washers every time you change the oil. Annealing them softens them up again.

To anneal them you simply heat them with a torch until cherry red, making sure you move the flame around the washer to heat the entire thing, and then quenching it in water. 

thanks for input, i will probably try to modify gasket as mentioned by Konrad.

must admit i never thought of annealing gasket, because it was new it should have been ready to fit?