I bled the brakes, brake pedal is stiffer for a few days, goes back to being loose again after a couple days. It's definitely losing pressure. Checked all the lines, etc. 99 S70 with 148k. Most likely original master cylinder.

 

Sounds more like the brake booster and not the master cylinder to me.............Are you losing brake fluid? I'd check all the lines and calipers first.

 

I have not lost any fluid. I just replaced the ABS module due to the original failing and causing me to intermittently lose my speedometer though. Brakes feel a little stiffer, but I want a rock hard brake pedal. It may just all be in my head honestly. Although, the master cylinder may be worn out.