Super Oyster crown replacement

[Douglas Davies]

I have worked on my own watches for many years, but am new to Rolex. A friend gave me his father's Oyster Perpetual 6084 to service. The watch was purchased new by his father in 1953, serviced on 4 or 5 occasions, and put aside for another watch in the 1970s.
The watch has a crown with an underscore crown marking. When I went to replace the o-ring that I expected to find inside the crown tube, I saw that the crown tube has a black plastic lining that is a snug fit on the crown, but the only seal is the gasket inside the crown. The tube also appears to be pressed in, but I am not sure of this. The watch is marked 1.53 on the inside of the back, so I am wondering if this was originally a Super Oyster crown. I have seen written somewhere that after Rolex discontinued using the Super Oyster system, the service centers would retrofit a screw down crown on watches that came in for service. I have no idea if this is true, but I am wondering if this is one of those retrofitted crowns.
Any thoughts would be greatly appreciated. Thanks.