I have an issue with the nc21, just finished refitting the engine yesterday had a quick blast around 10 miles to check everything was good and it was ok but today i went to collect my wages and when i got there i noticed there was a puddle under the back wheel and the wheel and swingarm was wet, i checked the coolant level and all was fine and it hasnt happened since!

BUT the left oil cooler pipe that bolts onto the engine was leaking so i got back and got the spanners out to tighten the two bolts up, the inside one tightens properly but the outside one is refusing to tighten to the level of tightness the inside one did, would this cause oil leak, i thought the o ring would keep it oil tight!

Its mounted to part of the crankcase so performing a good repair to the possibly messed up thread could be very difficult and i realy dont want to take the engine out again as its a pain in the a`$e to get in and out!

The other idea ive considerd is liquid metal but thats a last resort as its not good practice and it looks awful!

Remove the pipe with some rag under it / bowl. i cant remember if a lot will come out with the engine off.. should leak too badly.. inspect the hole, make sure the o-rings in good condition, they go crap with heat, always best to replace.

When re-fitting make sure it sits in flush else the bolts wont tighten up properly.

hopefully you can get a seal.

i had one leak, needed new oring and re fitting, been fine ever since

When you turn the bolt in does it come to a dead stop,
Or does it keep turning,if it comes to a dead stop it could be one of two things,either the bolt is to long and is hitting the bottom of the hole or it's a shanke'd bolt with not enough thread that would prevent it from ,tightening sufficient enough to seal the o-ring.If it just keeps turning the the thread is shaged,forget the liquid metal it's shite,
with the bottom rad and poss i exhaust pipe out of the way you should be able to put a helicoil in it,
If you don't do this job right it could mean a fucked motor,because if that pipe was to blow off you would lose your engine oil in seconds. (This is not a major job).

im going to rest from the frustration of the thought of thinking everythings fine only to relise the gods of oil spillage have rain'd down upon me like a plague of locests

And then pick this problem up tommorow!
the helicoil route sounds like a plan of action as it means i can do it with the bike assembeled still i think as long as no swarf get into the oil passage ways a strong magnet may help!

I don't think the bolt goes through into the sump,But not sure i can check some NC30 cases i have,