[Surly Mermaid]

I bought my Tiara 3900 Convertible new in 2007.  It has Cummins QSC 540 hp engines and ZF 305 transmissions.  In June of this year, my stbd transmission failed.  At cruise, the stbd tranny would fall out of forward gear into neutral.  Mechanic came to boat and found lots of metal shavings in the mesh filter of the solenoid.  Not good.  Transmission was taken out and replaced.  The forward clutch pack was hammered - all the outside teeth were gone.  With new transmission installed, took the boat out and it still fell out of forward gear at cruise.  Mechanic came back down and found a faulty plug on the top of the tranny was the problem.  We assumed the transmission had failed because of this bad switch. 
However....6 months later, my port transmission is now needing to be replaced.  I noticed the prop shaft spinning at idle in the slip.  The stbd prop shaft did this also before failure.  Mechanic came down and found lots of metal shavings in the mesh filter of the port tranny solenoid.  And this isn't the result of a faulty part.  

My question is, how many hours would you expect to get out of these ZF 305 transmissions?  My boat has 2250 hours. This seems way to early for transmissions to be failing.  


Thanks for your input.  

Ali Johnson
"Surly Mermaid"