I would definately check the simple stuff, like tranny fluid level and maybe bleed the clutch. There should be a plug on the side of the tranny to check the fluid, probably wouldn't hurt to change it while youre under there. Does the clutch feel good? What year XJ do you have? If your synchros are bad and you have the older Peugeot tranny, I wouldn't waste money on it, just replace it with an AX-15 or NV3550. If it is the synchros, you could probably replace them yourself if you have worked on cars much, manual transmissions are really simple.
'06 Wrangler X, 4.0 Auto, 31" Kumho MT's on Black Cragar v-5's
'92 White XJ Laredo, 3" Lift, 33's SOLD