Caterpillar Transmission slip??

[saltierdog]

my boat is a 86 tiara 3600 open with twin cat 3126 and cat transmissions

last night while diving i did an underwater inspection and noted that my starboard prop freely moves about 5 degrees back and forth and then there is like a clunk sound feeling as the regular resistance is met

any ideas how serious this is and how to fix ?

I checked the oil and its normal color and level (this transmission has a few loose bolts and leaks a bit of oil but the CAT mechanic told me 4 years ago that i would have to take the engine out to tighten the bolts

I have dripless shafts if that matters

thanks
joe