I cannot shift gears, transmission is stuck in neutral

Unfortunately this means you are in need of a clutch replacement. Here is a guide that will help with this:

https://www.2carpros.com/articles/clutch-symptoms

https://www.2carpros.com/articles/clutch-doesnt-work-sometimes-or-not-at-all

I am sure the slave cylinder is leaking and you could replace this but it doesn't make sense to remove the transmission and replace it and not replace the rest of the components because they are all right there.

https://www.2carpros.com/articles/throw-out-bearing-replacement

So when you do this, it makes sense to do it all at one time.

Here is a guide that covers this:

https://www.2carpros.com/articles/how-to-replace-a-clutch

https://www.2carpros.com/articles/pilot-bearing-replacement

I attached a lot of material. So run through this and let us know what questions you have. Thanks