1994 Volvo SX out-drive slips while in forward

I have a 1994 5.0L Volvo with an SX drive on it.
Two summers ago it started having issues going into forward, it would go into reverse no problem, but in forward the engine would just rev. The marina near me suggested I drain the lower unit and refill, I did so and the lower unit returned to working as intended.
Last summer it happened again. It goes into forward, but doesn't lock in, it spins enough at idle to move the boat slowly forward, but as soon as gas is applied the engine just revs. I tried adjusting the cable, but it didn't help.
This winter I took the drive apart enough to get the clutch cone out. One side has nice horizontal lines, the other is almost smooth.
At this point i'm assuming the clutch cone is the culprit, but I can't find a replacement for it. it is stamped with 873312, but that number is out of production.
I have contacted a few repair places, and they either never call back, or one told me I had to replace the whole drive train. Volvo's customer service has been even more useless.

Does anyone know what the replacement part for the clutch cone would be?

Have you checked the hub in the prop? Does it have a drop in hub?

Correct oil in drive???
Proper adjustment of the shift cable and hence full engagement?

Prop hub is in good shape, it has no problem with full power in reverse.
filled with the proper oil
shift cables were adjusted as well

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ChrisCraft007 said:

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The transmission's part that slides up/down and makes contact with each gear cup is the sliding sleeve.
Once the sliding sleeve senses friction against a rotating gear cup, it should pull itself further in towards full "lock-up".

Wrong gear oil, debris within the oiling groves, etc, can cause what you are describing.

Does anyone know what the replacement part for the clutch cone would be?
In order to replace an entire cone clutch assembly, you would be looking at purchasing a complete set of transmission gears along with the sliding sleeve.
If by chance your sliding sleeve is bad, keep looking...... someone out there has the correct sliding sleeve.

Click to expand...

re: "shift cables properly adjusted." Maybe so, however, the adjustment procedure is done while shifted into reverse, which has the shift cable fully retracted at the drive end. This adjustment can be done correctly EVEN IF the clamp that retains the shift cable jacket to the drive housing is loose, missing or incorrectly retained. If this shift cable clamp is not correctly installed, shifting into FWD, which requires a full extension of the shift cable, will not index fully.