It's your brushes the part number is JX118 and they are $3.22 for the set. While you are in there replace the Drive End Bearing 60AMP Hitachi #203FF for $6.58, Then go over to the Vacum side and replace the $2 worth of "O" rings and you will be like brand new.

86 Isuzu Trooper TD 5 speed
82 Isuzu Diesel I-Mark
86 300 SDL MB 126
85 300SD MB 126
82 300 D MB 123