Yes, I have seen similar repairs, in the Imperial era they used a resin of some sort, sometimes applied in a strange way, like pellets, but also like a bakelite fill too. Very hard, black but resin like, sometimes it is found cracked in places due to age or heat.
This style is more interwar and nazi period, in the interwar period the Germans were broke, coupled with Versailles and a left leaning government much of the time (even under Hindenburg I wouldn't call them very conservative, though fiscally they were typically German - "responsible" with money) they weren't re-armament happy and kept the military on a tight budget. Which meant very frugal with re-using materials where possible.
In the nazi period they were careless with money, fascists, like obama, do not care about the "peoples" money and spent it recklessly. Early on, before they had complete control, you see some frugality because there was only so much money they could spend and unemployment was the biggest threat to their staying in power. Rearmament required things be done in stages, they started with facilities (barracks, airfields, infrastructure) and skimp on some of the things you would think would come first. They went nuts on airplanes for instance, but surprisingly training aircraft by a large margin (makes sense but as nazis are stupid and enamored by "power" you'd think they would have started with bombers and fighters.. probably only went with trainers because someone explained it to them with a crayon..). Rifles they spent a lot of money on reworking and upgrading rifles, lots of salvage but new barrels, stocks and r/s and wide bands were made new. After they were tight as a tick in Germany's flesh, they went wild with rearmament and salvage dropped out of style, but with the Gewehr98 they sort of had to keep with salvage awhile longer as they stopped making ordnance spares before the war began (1938-39). That is why you see such crude repairs and a lot of "conversions" to 98k during the war (really just scrapping rifles by 1941, reusing the receiver and built as a K98k, the balance parted out for those rifles that can use the remaining parts...)
I didn't notice before but the old stock number has been cancelled with zeros like your other depot guns.