Sorry to hear about your problems .... I can try to help.
How did you determine your 1st gear is "out" ?
6th gear & reverse ... not impossible (as nothing is), but HIGHLY improbable - has never been done & would cost you more than 20 brand new transmissions.
"Bullet Proofing" a transmission ... hmm ... something can always break, especially with the shift fork design of these bikes. We have one of the industries best building these trannys & there is still things that can & do go wrong.
What is your bike doing ?
From my experience, with a trail machine, even beating the crap out of it, the most common issue that arises is bent forks.
If/when you get into it, besure you install the "revised/improved" forks from the more recent production years.
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