enclosed the part of Belt-maintenance in the MG08 instruction-Book,
not mutch information,
no information abut soiled / oiled Belts

I try a translation:
the Belts have to be cleaned careful by the Belt-Cleaning Brush (describted as special type; 12cm long; 4cm with, strong brushes)
Wet belts let the cartriges stick very tight, so the fire-rate goes slower or the fire stops.
Belts should be protected against water.
Are Belts get wet: dry it and strech the pockets bevor using.
Also the Belt should be protected against water and Oil.
Greetings
Alpencorps