metal bits in diff fluid

just got home from getting my oil changed by a independent garage(guys a f'er) i asked the dumb kid to check my differential oil. he pulled out a sample and showed me it.when i saw it,i was like huh?it had bits of metal particles in it! so anyhow,the kid starts telling me how the oil is good,never seen it clean like that(by now im thinking i am getting the royal screw job) i told him thanks and left.now i guess my gears are getting eaten badly,or is this normal? is there any way to prevent this? some info: 1985 amc laredo, all stock, 233 000 km (or 136 000 miles) dana 30 front dana 35 non c clip rear,it does have a trailer hitch but i have never towed anything.(i have owned it for 6 months)tranny (i think) gives a little kick when shifting (not all the time,only when cold)tranny fluid is dex 111(couldnt find dex 11 at canadian tire, tranny was almost empty when i got it) tranny is the 3 speed auto tourque flight,v6 2.8l motor, transfer case is np 229 selec-trac(front drive shaft removed,no idea on its fluid status)

so sorry about my life story, what do you guys think i should do? it is my dd and runs great,outdoor mechanic here so gotta wait for some nice days to do anything! thanks in advance guys!

open the diff and check the amount of wear on the gears and then decide what to do.

I would say the diff fluid has probably never been changed on the axle. I would definitely take the cover off and drain the fluid and hit the whole diff with brake cleaner.