6NZ rear main seal only leaks once trans is bolted up...

So, here's the deal. Took truck to Kenworth to have a pick list of stuff fixed. Front & rear seals were among the list that included new 13 speed trans (Weller) and clutch. Everything resinstalled and oil leak from rear seal was worse. Unbolted and slid trans out, found that guy who inframed engine OMITTED thrust washer so crank was moving horizontally almost 1/4 inch. Dropped oil pan, rolled in thrust washer & all new bearings (mains & rods). Tech says "Youre lucky as hell - no additional damage". Reinstalled oil pan, new rear crank seal, installed housing and flywheel and run the engine - smooth and dry. Whew! Well, they reinstalled trans today and we are back to leaking engine oil from rear of engine. They are scratching their heads, and so am I...... ANY IDEAS OR THOUGHTS ON WHERE THE FLIP THIS OIL IS COMING FROM? Anyone had a similar issue? If so, what fixed it? TIA......

 

This is at a KW dealer in Mobile, AL

 

Well, it's fixed. Old school bell on a new school trans. New trans has 2 extra bolt holes that bell doesn't have. All oil looked same because engine was just serviced!! Had there not been a misdiagnosis, trans would not have been dropped and missing thrust washers would not have been found. $3000 now saved $30000 down the road!! Thanks for the replies!!