I have done 3 T cases and never had this issue. Try hitting the upper plug with some PB Blaster a few days in a row, and you will get it out.
Case is aluminum and plug is steel. Should not be in there forever.
2004 Durango SLT AWD 5.7 Hemi Flame Red with 3.55's (Mine)
05 Dodge Grand Caravan SXT 3.8L Linen Gold Pearl (Hers)