So John have you taken your car to a garage to diagnois the problem...
I spoke to Greers this morning and guess what they've just sold a hawkeye 5 speeder earlier in the week..they also said the hawkeye has different rear diff ratio to eveything else which means that you will either need to get hold of a haweye 5 speed box or another 5 speed box with matching rear diff.
Or rebuild your own box.
Either way they will need to look at your car first to see what is wrong with it.
But probably your best(cheapest) bet is to try for a warranty thingy.