L-drive sound like its full of rocks

I have a 1990 85 hp Capri inboard outboard. when i first put it on the lake today it went into gear fine and took off. within a couple of hours, i started losing RPM's and when I slowed to go wake less, I could hear a rattle. at that point i no longer had reverse and no matter how many RPM's, I had little forward thrust. any ideas?

The "rattle" sounds like either the u-joints or a gear in the lower unit has broken??
The "no forward thrust" sounds like the prop has spun the hub??

Check the gear oil for metal shavings and chunks?
Remove the prop and check the hub for rubber pieces, or try marking the hub(2 lines) and put it back on and
go for a ride and see if the marks move?

The u-joints? Not gonna be easy to check. Get a parts diagram and start taking it apart.
You can try u-tube for repair video's.

If it's the lower unit? the ones for the 85-90-125 will fit.
They all should be the same gear ratio.

I drained the oil, it seemed ok , no chunks of metal, but a little gritty. Pulled the prop, rubber seems to be in good shape. doesnt even look weathered. looking for a parts diagram now. getting ready to take it apart.

Look on eBay for a factory manual.
The aftermarket books like Clymer or Selock don't have enough info to help.

https://www.ebay.com/itm/Force-Outb...846983?hash=item2ad0829c07:g:-oQAAOSwl5NdLgLi

I recall this ---L-drive ----system getting awards for best new boating " thingy " long ago for some reason.------But today it is full of NLA parts.------Universal joint assembly at $500 or so.-------Get rid of this nightmare.------Modify boat and stick an outboard on it !!

I didn't want to scare him with the HORROR stories.