Jeff,
There's an old adage, which goes something like: every day for a week; every week for a month; every month for a year; and (roughly) every year forever. I don't know where this comes from, but I expect it dates back at least hundreds of years, and these people knew what they were talking about.
If you cut, shape, and oil a piece of wood, it's going to dry out quickly at first, but stabilize over time - especially if you help it along in the early stages. It's easy to see, particularly if you watch places where the end grain is exposed (like cutouts by the neck): you can just tell when it's getting thirsty.
There are others listening here who can perhaps give you better advice on oils, and Michael's offer of the original owner's guide is probably the best place to start. Personally, I've been nurturing a Carvin for ten years (fretless ebony fretboard/maple thru-neck/solid Koa body wings/tung oil finish) with the ubiquitous Old English Lemon Oil, though I recently switched to Jasco - Alembic recommends this for their fretboards. It seems like it might be slightly higher quality, hard to tell - though if you get Mica talking, she may start rhapsodizing about long chain molecular structures, and send you off to a health foods store to buy some pure lemon oil... (but maybe I'm remembering that wrong?).
It seems to me that about two or three years ago, it turned a corner and is now starting to absorb more oil than it loses. I can see more depth in the grain, a more healthy glow (though a bit darker, which might have something to do with the Old English), and I also think it sounds better... but this of course is all highly subjective.
I also vaguely recall that - back in the dark period when this discussion was hosted on Yahoo - there was sort of a cult following of Jasco *lime* oil, but it's not clear that exists anymore (Palembic: that would be the green one). I think part of this had to do with it being more effective at cleaning out gunk around the frets, but that's not an issue for me... not sure whether it was truly better for the ebony itself.
I'd like to hear what you learn from the manual (or other opinions that are out there), but my guess is that for a Watco/linseed finish, any decent lemon oil would be just fine. If you needed a more drastic resurrection, a heated linseed treatment might be worthwile, but that can be tricky and I probably wouldn't try it myself unless I was desperate, and practiced on something else first.
It sounds like yours is in nice shape, so look at it in a good light, apply some oil, let it sit for about 15 minutes, see how it soaks in, wipe off the excess, look at it again, and use your judgement. I think it will be clear.
For my new bass, we spent some time talking about the tradeoffs between traditional tung oil, and a more contemporary polymerized version which they prefer these days. In crude terms, it's basically the same as tung oil with a catalyst, so that it sets and eliminates the risk of becoming gummy. It sounded like they had some specific recommendations on how to maintain this - *not* with generic lemon oil - but I'm waiting to follow up on the details until my bass is ready.
Sorry for being long-winded (again), but as you can see I really like wood, and the craftsmen/people who make fabulous instruments out of it. I can't say that I've ever seen a nicer polyester finish than the people at Alembic produce these days, but to me that's still plastic - and long before, they knew how to do the natural thing at least as well.
-Bob
