The Russians can’t replace much of their weaponry because the Russians have destroyed the Ukrainian factories that produced most of that equipment.
It’s really unknown at this point if Russia actually has extensive reserves or stores of weaponry because so many of their pre-1991 armories have been deactivated or abandoned. Lots of videos on the net to support this observation.
Russian arms sales over the past thirty years have drawn down much of the vast armories of the USSR. It’s been easy money for the oligarchs and the government to just pack up and sell stuff with practically no overhead.
So what really remains of all of that stuff? And how can Russia replace it when 1) most of the USSR factories were in Ukraine and 2) so was the know-how to make this stuff.
Yes, the Russians can make an indeterminate number of missiles of questionable efficacy, but can they produce warships? Tanks? Armored vehicles? Artillery tubes? Artillery ammunition? Bullets?
So far I’d say no because I have yet to see any claims (even from Russia) of newly produced supplies of military goods.
Sadly, Russia just needs weapons that can kill children. That is the Russian way of war for generations. They don’t need advanced weapons to do that.
“So what really remains of all of that stuff?” (Soviet stockpiles of artillery shells).
That is really the big unknown.
As you point out, they may have been selling that stuff off under the table for 30 years. We know they have been selling some openly.
It is possible that they might run down the stocks, and have to fight hand to mouth, based on what they can produce. That would certainly be a big step down from the rate of fire they were massing in the Donbass.
The Russians have already fired 7 million artillery rounds in the Ukraine, which is a Hellish amount. They are wearing out barrels, and losing trained crewman. Something will break.