The piece that goes into the back of the gearbox, the yoke is the same thoughout all models.Tailshafts length is different from EA to EB then EB to EL is the same length but has different flange at the diff and sizes of tailshaft is shorter about 1100mm from memory.The EA has the same configuration as the XF,4 small pissy 6mm bolts which attatch the flange to the diff.The EB-EL has 4 meater 8mm bolts at the flange thus stronger.There is no real way of getting the two mixed up as they have totally different flang setups and length is too great to reach.The only tailshafts that can get mixed up is from EB to EL as some have a balance weight at one end in auto models,some aluminum and so forth.So I think they are pulling your leg.
It is a common problem for that to leak.They probably replaced it with a steel bush instead of Brass and you will be back to them in about 2 years if the steel one is used.Check to see which type they put in.
On another note you live Queensland,do you know about the EA-ED meet happening on August the 11th??If you go to Meets and cruises of the E series network there are details regrading this meet under Brisbane Meet.If you have any troubles or want to know more Email me at firstname.lastname@example.org
New Appointed QLD REP 4 EA -ED club.