I bought my first one in 1977 a new mapleglo 4001 w/case for 479.00 at Wurlitzer's in Boston. I could not get enough presence out of it, sold it a few years later and stayed with my Fender P basses and then bought a 1980 4001FL for 500 bucks in a music store in 1990, I then bought a white with black trim 81 4001, on and on. It took me a long time to realize that the cap was sucking all the life out of the 4001's and it was a Eureka moment when I finally tried the simple reversible mod. I tried it first on my 79 4001 mapleglo in 2003 which I still own and it was like, wow, my Ric is suddenly hear, I could hear the low mids which the cap scoops out and which gives these basses their presence (any bass actually). I've had so many over the years that a conservative estimate is at least 25, both 4001's and 4003's. The necks got chunky around 1996 and stayed that way until relativity recently, they are supposed to be thinner since about last year.
They took out the cap in late 1984 and put it back in a few years ago with a switch to put it in and out of the circuit, I had one and still hate the cap.
With 4001's if the nuts are digging into the back of the TR cavity it is because the strings are too heavy. Always push the neck backwards to take the tension off the neck from the strings forward pull as you tighten the truss rods on a 4001, also the truss rods are very light metal, if all of a sudden the nut won't turn any more at a certain point and the neck is still bowed it is likely that the threaded part has twisted and distorted the thread pattern, be careful you can snap the thread right off the end of the rod.
I always use flatwounds on all my basses including Rics, usually chromes. I now only own two Rics: a 72 jetglo 4001FL and the 79 mapleglo 4001. I plan on buying a new 4003FL since I have heard that they have finally got the side dot situation correct.