[IC27A] chronic stuffing box leak

[raphoe10188]

 I have a 1978 shoal draft 27 with a 1 cyl yanmar replacement engine.  In the 
past year the stuffing box leaks a lot after running the engine for a while.  
Mechanic supposedly replaced the stuffing, helped for a while but it is 
starting again. Tightening the nut helps for a short while.  Where do i start 
looking to solve the problem?