GB, I wanted to add the following two points.
First, Enstrom released a newly redesigned main rotor drive shaft that has a thicker wall, which cured the previous track and balance problems. I understand that new machines come with this shaft, and it can be fitted on older machines. Maybe you can find a ship that has this new rotor shaft installed.
Second, maintenance on an Enstrom can be a little tricky, as some of the procedures (drive alignment procedures in particular) are very precise. If you're thinking of buying one, be sure a good maintenance shop is located nearby, staffed with folks who know what they're doing with Enstroms.