I do recall that some years ago on the original bolkows there was a tail flaexing issue, that resulted in an uncoupling of the tail drive shaft, these incidents occurred around 6000 airframe hours, and resulted in the splashdown of G-AZOM 5 miles off skegness during one year. I believe modifications were made to stiffen the tail boom at the point it joined the rest of the helicopters main body. Other than that I am not aware of anything else, some bolkows are well over 20000 hours currently.