Mine has been howling for years. You can ignore it a long time if you wish. Although I did research a couple of options. The 8.8 rear end on the X is conceptually the same as the 8.8 mustang. This is not an on car rebuild.
Check these posts out for 8.8 rebuild:
http://www.pirate4x4.com/articles/tech/billavista/Gear_Setup
http://fordmustangcar.com/repair-and-manual/trakloc-install
http://www.mustang50magazine.com/techarticles/m5lp_0705_traction_lok_differential_rebuild/
http://www.f150online.com/forums/20...le-seals-bearings-your-04-f150-lots-pics.html
http://www.kitcarinfo.com/IRS_Gear_Swap.htm
http://www.explorerforum.com/forums/showthread.php?t=336162
http://www.corral.net/tech/drivetrain/gears.html
http://www.explorerforum.com/forums/showthread.php?t=144780
If that doesn't bother you then, I also priced out the parts to do the repair myself. These prices are about 18 months old but should give you and idea of the costs. Keep in mind this was for my 3.73 rear end with LSD.
For the clutch pack TSB
part# 6L1Z4947B for 129.57, 7L1Z4A109C for 30.46, W710084S439 for 7.36, 1L2Z4B422BA for 15.31, F3TZ4121AA for 8.23, you'll also need the gear lube and friction modifier from Ford
For the ring and pinion TSB you'll need part# 8L3Z4209N for 306.98, 2 part# XW4Z4221AA for 16.47 each, and 2 part# D9AZ4222A for 12.44 each.
I talked to a mechanic that specialized in drive train repairs and they said it would run 426.00 labor for them to do the ring and pinion and clutch pack, which would also include replacing all the bearings.
You can also get mustang parts for the ring & pinion issues. If rebuilding yourself this appears to be the most cost effective solution by going with parts from Ford Racing. I was look at the M-4210-B2 or M-4210-A kits. The $74.60 kit will be the m-4210-b. the b2 sells for around $83. The kits are the same except for the b2 kit has the newer style pinion bearings( known as the "high torque" bearings) According to the parts place either kit would work fine, but you may need the side bearing races mentioned.
$126.50 for the ring & pinion
$64.90 for clutch packs
$74.80 for the bearing set
$32.96 for a pair of Ford OEM side bearing cups. The ones in the kit do not always work in the Explorer rear ends, but is still well worth the $74. If you did not need the cups, of course they can be returned.
$56.90 for a pair of half shaft seals (OEM)
I also checked out a former forum sponsor and they offered a rebuilt pumpkin which was complete rear center section diff 8.8/3.73 posi - $ 1195. plus core $ 300. includes shipping both ways and comes with a 1 year unlimited mileage warranty.
Another mechanic suggested it maybe cheaper to install a OEM or a Jasper rear end on the long run, due to the 1 for 1 replacement warranty.
But before you replace the clutches change the fluid, add a tube of posi trac additive and then make a bunch of tight right hand turns and left hand turns in a parking lot! Doesn't cost much to do that.
Good luck.
