Funny Darren, but what is a BOL Roto-Swirl? They all were white from the later 70s forward, as well as many in the mid 70s. Once the Super Roto-Swirl came out in 1963 (the standard was discontinued at the same time approximately), I have never seen even a tiny difference in the Super Roto-Swirl from that point until the end of the commercial BDs in 1987. The side ridges in a bakelite Super RS were more rounded than in the polypropylene plastic version, but that's all I have ever noticed.
Personally, I would have left the machine with the RS in it. Not a big RF fan.
Oddly, in only one case in early 1979, a Sears catalog described a 70-series machine as having a Super Roto-Swirl, then it separated that machine from the next down, which was an upper 60-series model, which had a "regular Roto-Swirl". It was odd enough to have a Roto-swirl in a 60-series model, but I don't think the agitators were different except perhaps maybe in their color. I have never seen these separated like that though, before or since.
Gordon