1996 Honda Civic Clutch losing pressure

My civic has recently been having problems with shifting gears. It seems like my clutch has lost responsiveness and I need to pump it to get pressure. The clutch used to have a nice wide range of engagement but lately it engages all at once at the bottom of the pedal. When I pump it for a few seconds I gain about half the range I am accustomed to. I believe I have a hydraulic clutch so perhaps this is a bad seal.

Also, it has recently gotten very cold here and this problem has gotten worse with the drop in temperature. Maybe it's coincidental, I dunno.

I have some minor mechanical experience, swapped out power steering pumps, water pumps, radiators, starters, alternators and such. My questions are what is causing the loss of responsiveness and compared to the aforementioned items how hard is it to replace a master or slave cylinder, if that is what it is?