Over time, Alfa has made many modifications to the internal components of the 101/105 gearboxes to improve durability and reduce maintence needs. These include some things that required a change in the type of lubricant. Early 101, 4 speed and later 5 speed gearboxes used syncro rings that had a series of groves cut around the outside of the rings. These older rings are a "non moly" ring and is lubricated with Dentex or one of the substitutes. These rings would wear and lose grip on the inside of the hubs (particularly second gear), causing a grind when shifting down into second. Sporting driving, double clutching on downshifts, still took a toll. Labor was relitively cheap and the bad ring, or ring and hub could be replaced. As time went by, (and labor rates increased) these earlier style rings were superceded by moly rings and hubs. These rings are dark grey or blackish and have a rough sandpapery surface. They require a more modern lubricant than Dentex for long life. They still wear in time, though slower, requiring less transmission R&R. Though Dentex can be used with the moly rings, it is a poor choice. If the moly lubricant is used with the old style grooved rings, they have no bite in the hubs and most if not all syncronizing effect is lost.
This is very simplified as the purpose is just to explain the differences and results from the wrong lubricant. Older non moly boxes can be converted to use the newer moly rings and hubs at a cost
I hope this helps.