OM15 You are correct with regard to the leaking hyd seals( lower jet pipe area ) and the mod. programme to rectify the problem. I spent many "happy hours"
on 431 MU engaged in replacing those seals at Gutersloh ( happy days ! ) as part of a mod programme which also involved replacing the outboard drain collector box and also the fuel system seals. The tolerances for the latter around an expansion joint were so tight, they were X-rayed after fitment to ensure the gap was correct. There was, as I recall, also replacement of some associated bracketry due to vibration cracking.
To give you an idea as to the depth of the programme, a team of 5 would work for 14 days solid ( other than for rest.....and the odd beer or two ) in order to complete the programme.