Flushometer Sloan Gem-2 - Help needed

Hi,
I have a Sloan Gem-2 and when i push the handle down to flush it slowly fills the bowl with water but dosnt flush.
If I pull the handle up and hold it for a couple seconds it fully flushes and its also dripping some water from the handle at that time.

I was thinking I had to put in a new handle assembly kit but im not sure, nor do i know if its easy or not.

Im having some doubt its the full handle assembly kit and not just a new seal to stop the leak and a tweak of something because of the following, A while back I had a similar problem with the handle not flushing and the maintenance worker in my building happened to be in my apt. for some other repair and I told him the toilet problem and all he did was adjust something with his basic tool to solve the problem for a couple of years. (No new parts were installed that i know of) Im not sure exactly what he did because I wasnt watching nor did I ask at the time.

Ive never worked on a toilet before nor any other plumbing but Im trying to learn how to repair my own fixtures.

Thanks for reading and for any help provided.