v8 is great

hi i have an audi rs6 c5 2003 4.2 v8 twin turbo i had a problem with the gear box first off it was slipping when hot in drive mode not in trip or paddle so i took to garage he said to buy new gear box oil and pan filter also gasket this cost a bomb then when i went to pick the car up it wasn't slipping its now making a silly metal against metal sound when changing gear really weird even in trip and paddle now very confused any one had this problem thanks in advance seb