Transmission question

[makesure]

Hi!

So I bought an 88 Cooper 10m this year with twin inboard Mercruiser 5.7l with Velvet drive 71C drives. Over the last few months, I've noticed that the port shifter was getting stiffer moving in and out of gear. Then yesterday, I was out for a short cruise and the drive all of a sudden started to squeal loudly and I started pulling to port. I quickly went to neutral and checked the engine room. Everything looked fine, the engine was running smoothly and the were no outward signs of an issue. I tried putting it back in gear but it wouldn't engage forward or back.
Has anyone had this happen? How pricey of a repair am I looking at?

Thanks!

 

[alldodge]

You need to pull the drive to start the investigation

Edit: woops you said inboard

Assuming you have velvet drives, first check fluid levels, and color. The fluid should be clear and red

If its dark and black or low oil level the clutches have burned up

 

[Bt Doctur]

You have been doing your inspection routine checking before leaving port? oil levels, water leaks, strange noises, etc.
Locking up a shaft can be from no oil/ contaminated oil in the transmissiion to simply a rope wrapped around the prop.