You need to contribute to the discussion. A photo (or a link to a page with a photo of a similar-looking instument) would probably make it a snap. But I'm curious, so I'll put in my 15 minutes.
First, the pot
(potentiometer) problem. Yeah, Washburn's controls were the main suck of the basses; I have two with the pots frozen solid. My guess: yours froze too, & "someone"
cranked on it just a little
until it loosened up, which means ripped the shaft loose of the contact carrier -- it's possible that pulling up on the knob will pull the shaft completely out.
The pots are stock hardware, & a replacement will cost you $5 or less from Radio Shack, Musician's Friend, DigiKey, Mouser... well, just about anywhere. All you need to specify is bushing length
(mounting through wood, probably 3/8"), shaft
(probably knurled split), terminals
(pointy spikes for printed-circuit-board mounting, open "O" for wires), & taper
(linear or audio). As to that last:http://sound.westhost.com/pots.htm#markings
The hardest part of pot replacement is getting a good solder joint to the case; after that, it's a breeze.
Since the pot's been broken, you should also check to ensure that whatever it's soldered to isn't also messed up -- one of my basses came CHEAP because the previous owner tore five wires & a connector loose, all wrapped around the pot. (An hour of work & I gained $200+ on the resale.)
Washburn hasn't been much for fretless -- offhand, I find an AB, a Taurus, an XS, an SHB, & (maybe) an old B2 -- so a FIVE-string fretless seems VERY unlikely. If the fretboard has lines, it's been defretted, post-factory.
Not only was 1999 a big transitional year for Washburn models, but archived info is a bit erratic. The 1999 price list has the Bantams comprising RB & XB models, with similar shape of body & headstock. (Weirdly, it also includes the DB2000 Dimebag, which is a Vee shape.) Unless your headstock decal says MADE IN U.S.A., it's got to be a 105 or 125 or 500. That'd be a very late XB500; the 400/500/600 were suddenly dropped after one last big push, so I figure they just made a pile of generic BANTAM plates rather than specific to the model.
(Washburn seems to hire casual glue-sniffers, so can be very inconsistent in numbering: the 125 is the upgraded
five-string 120, & the 500 is the five-string 400.)
I hope this helps. Photos are always appreciated!! (They increase traffic to this site, too.)