2003 F-150 Supercrew FX4, 31,000 miles 5.4 Auto, electric shift 4WD

I'm takin' my truck in to the Ford house. 4WD is intermittent. Quits when I really need it. Ford mechanic says it's "probably" the shift fork in the front differential. Vac solenoid strokes good and full stroke. Good vacuum. 4WD tries to work sometimes, then quits when it gets just a lil' bit deeper, then I'm stuck.... I'm told, that the shift fork is steel, but, has lil' plastic nubs that do the shiftin'. 'n when them nubs get worn jus' a lil', they quit workin' too good. He said he's had to replace a number of 'em. I asked how often this has to be done? He said, "Well, hope ya' got the 'stended warrn'ty...."
Anybody got 'ny good idears for fixin' this lil' problem jus' a lil' more permanent?
I may be a little premature, puttin' it in the shop tomorrow, but two of the ford mechanics checked it over, had it up on floor jacks, 'n throw'd down a creeper fer me t' come under 'n watch 'em. Engaged 4wd, solenoid stroked full stroke, 'n then the front wheels still turned either direction by hand, not engaged like they said it ota' be. They convinced me.... Said they don't know of a different fork anywhere.... Lettin' warranty do the repair for now.

bobvanzant@usaonline.ent

 

I have also been experiencing 4x4 problems in my 2003 f-150. I have narrowed it down to the front diff. I am wondering what is involved in fixing this sort of problem. At this point the truck is making some nasty sounds coming from the front end and 4x4 is a no go. I replaced the actuator, which was bad. I imagine the damage has already been done inside the diff. It sounds as though somthing is binding in there. Any advice would be greatly appreciated.