I've mentioned this several times, but it's fun to talk about this maintenance stuff, so...
If I recall correctly, the fretboard conditioner ('lemon oil') is scented naphtha. It's the same stuff dry cleaners use to clean stains out of your clothing. It's wonderful for cleaning the surface of the rosewood, but don't leave it on. It should be wiped off after use, because it's a petroleum product and can eventually soften the wood. I think this is what Moondog was talking about. Use too much, and you can actually cut a groove into the rosewood with your fingernails (yeah, been there, done it).
It
appears to add oil to the surface, but that's simply drawing the oil OUT of the wood and sticking it on the surface; when that oil evaporates, your guitar's rosewood board is actually drier.
With my own RW neck PRSes in the past (I've owned several), wiping down a rosewood neck with fretboard conditioner does not act as a moisture barrier, and that the necks still feel a little bit "furry" after a few plays.
PRS used to recommend a furniture polish after cleaning with the fretboard conditioner. When I got my first PS I marveled at the slick finish they used on the ebony fretboards, and asked how they achieved it (this was 2013). At the time they were using boiled linseed oil and polishing it, after cleaning with the lemon oil. It was truly a lovely surface that lasted a long time.
Tung oil dries to a hard finish on the surface and resists moisture. I haven't asked PRS about whether to use it on a rosewood neck, so please don't take my word for it, I'd call them for verification. But it seems it might be worth a shot to solve your problem. Let's put it this way: If I had a RW neck PRS at this time, I'd try it, even at the risk that it wouldn't work, the caveat being that I could be making a big mistake!
I have a tung oil finish on the maple edges of my studio furniture. I've only had to redo the area where my hands rest and rub once in the 29 years since my brother and I built it, and that was earlier this year. See pic below.
On the other hand, the stuff I used has the look of a slightly glossy clear coat finish, but that may be because I used Minwax' Tung Oil, and not a different type. I have no idea whether the Minwax finish is pure tung oil or something else. But I can say it's pretty darn hard-wearing and impervious to moisture. I’d use it again, it looks great.
This is a pic of the studio workstation area and the furniture we built and finished; the maple edging is what I’m talking about. After 29 years it certainly has held up well. The surfaces are the maple edging, black painted oak, and the tops are black satin Formica. we fabricated the legs from steel square and rectangular tubing and welded and painted it. We did this because we were lunatics! But...29 years so far? Not too shabby!
