Volvo Penta HS1 transmission lost forward

Today we were running about 3500 rpm on our twin VP 41 series diesels in a 29' sportfisher. Then the rpms on the Port engine went up to 4500 and we lost speed. Checked and when in forward the prop shaft is spinning at idle but doesn't increase when the rpms are increased. When in reverse it seems to operate properly and shaft speed does increase with rpms. The transmission on the Port engine is a HS1 with 1.96-1 ratio. Any suggestions on what may be wrong and if we can repair the transmission or need to get it rebuilt or get a rebuilt one somewhere?
ps the starboard HS1a was replaced by the PO at a cost of about $8000 for a rebuilt gear, not counting cost for labor. We are very mechanically inclined.

HS1A gear fixed and working. Upon tear down by good marine mechanic found the forward clutches burnt and warped. Put in new clutches and works great now. Mechanic charged $1300 and parts were about $700.

Do you mind sharing who you used to repair gearbox? I need to get one of mine rebuilt and cant find a mechanic in my area of texas that knows how. Any info would be helpful. Thanks

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