first - THat guy who over hauled few month back must be accounted for... no mechnic is good enough these days, they just do work poorly and do not have proper tools whats so ever...
Ajkal k zamanay men parts kharab honay say zyada mechnic ki zyadati ki waja say bike ya gari barbad ho jati hay...
best is to sit on mechnics and super wise the final assembly, specially when the do final torque on engine main bolts ....
head, gaskit leakage is very common becuase they do not use torque wrench and just rely on guess work, some times the over torque it and damage the center case or some time they under torque it and which leads to thee kinds of leakkage...
I havent find a single mechnic who does assembly by the book.. they just do hathora work.. all of them...