I also have a Rossi 38 that I picked up in a Pawn shop. I was going to let my daughter use it, but my son discovered that occasionally it would not properly rotate the chamber. I just set it aside. I haven't tore it down to see what gives. Maybe worn pawl or ratchet.
@Elderberry I am thinking that MAYBE there is some foreign matter jammed up inside. Se,ems to me if it were mechanical,it would jam every time you tried to cock it.
But truthfully,this thread is the only place I have ever heard of revolvers jamming to the point where the cylinders wouldn't turn. Take a quick look at the shell ejection spur and see if it shows any sign of damage.
Is the gap in the cylinder crane tight and even when the cylinder is closed?
Try cocking it and then pulling the trigger on empty cases over and over how smooth the rotation and "feel" are while cocking the hammer.
This should give you a good idea of what to suspect when you pull the side plate.
BTW,my 44 Special snub gun is a Rossi,and I have never had an instant of trouble with it. Since I am a qualified gunsmith (or was back then,anyway) my plan before even buying it was to pull the side plate and "slick it up",but it was so smooth right out of the box that it didn't need it. To this day all I have ever done to it was clean it,shoot it,and carry it.
Another possibility just occurred to me. There is a chance the quality control at Rossi went all to hell when Taurus bought them out to eliminate competition,and the last couple of batches of Rossi firearms sold didn't go through the quality checks of the earlier ones due to the pressure of "get them out of here so we can balance the books and close up the shop."
After all,when the company is going out of business and you are losing your jobs because a larger company bought you out and have their own workers,there is not much incentive to do your best to produce a quality product,is there?