Is it engaging so low as to cause baulky gear engagement? I don't mind a low engagement point so long as gear selection does not become difficult. At least there is no risk of clutch slip. As you correctly state, air in the hydraulics can cause the low engagement point. Another cause can be a faulty slave cylinder although since you have already removed yours, you would have noticed if it was leaking. Worn piston seals in the master cylinder could also be the cause without showing up as an external leak. Maybe if we swap parts we might both get our clutches to engage at the correct point! Mine has had the reverse problem to yours of engaging very high in the pedal travel when hot. I will revive my thread on that topic when I get back to sorting it out. Let me know if you fix the problem with yours.
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.