No Resistance in Clutch - 2003 Hyundai Accent

Recently there has been little to no resistance when depressing my clutch to shift into gear. I have to push firmly all the way down to the ground before it allows me to shift, and in first and reverse it grinds pretty hard. (I've only done it twice!) I've talked to a few people and read a few things and determined that it may be a leak in my slave cylinder...since my clutch fluid resevoir was pretty low on brake fluid. I filled the resevoir to the fill line, and it seemed to be working alright...resistance near the top when depressing the clutch. The next day, it was doing it again - but the resevoir was full. I had an ex-mechanic friend of mine take a look and found no signs of a leaking slave cylinder, so we bled the clutch for air pockets. He said he got a few out and it went back to running perfectly. Drove it about 10 miles, and now it's back to having to press it all the way to the floor to engage.

I'm not sure what else to do, I'm going to take it in and perhaps just have them replace the slave cylinder anyway - but, I wanted to get some more ideas before getting reamed for parts/labor costs at the shop.

Any advice would be amazing.

2003 Hyundai Accent - Hatchback
193,000 miles
Replaced transmission 18-months ago
No other issues of note