I have had both problems with the gouging of the rotor.
piston sticking and pea gravel
With the temps so harsh and variations of being in the elements and then in a nice warm garage the moisture begins to come into play in the brake lines
at the calipers, lack of not flushing the lines will hang up a pad.
The pea gravel the city here use for traction at intersection, curves and ect.
It's a must for safety, but the pea gravel will work it's way in between the rotor and pad.
83 300 tdt wagon 230,000 mi
85 380 se 31,000 mi
85300 tdt wagon 90,000 mi
84 380 sl 57,000 mi
84 380 se 41,000 mi