I suggest having your brake fluid flushed and changed, not only for peace of mind, but to make sure its clean and working properly.
Also have brake hoses checked, a worn hose can expand too much.
Pedal depressing further can happen if pads are more worn.
If it were me, I'd change the pads on both sides, front and rear, and have the brake fluid flushed and replaced, and the system bled.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.