Well... thanks everyone for putting in the effort. MotorradMike first suggest top transmission bolts. I knew I had six in there and torqued correctly. One of the issues with a repair like this stretching over and three week period (waiting for parts) and a couple of late nights is I tend to forget what I have done. The bolt in question had gone missing for a short time while the transmission was being install to the engine. I have a great selection of high grade bolts at home and I replaced it... later found the missing bolt and forgot what I had done. Upon re-checking this morning with a mirror and flashlight I noticed one of the top two bolts was a black oxide colour not silver like the rest. Then it hit me... I remembered what I had done.

I can't believe how may of you guys were right on the money with where it was!

Many thanks!