This error occurred at SASCO, just a stones throw from SIAEC. (not the one your after UK Subs) but it did involve JAL. Unfortunately the original link is dead.
It happened in 2005.
http://asia.news.yahoo.com/051221/kyodo/d8ekgjt00.html
Wednesday December 21, 3:53 PM
JAL B747 jumbo in sky for 7 months with engines on wrong side
(Kyodo) _ Japan Airlines had been flying a Boeing jumbo jet for seven months without realizing the plane's left and right outer engines had been placed on the wrong sides during maintenance in Singapore in February, airline officials admitted Wednesday.
Some components of the engines are required to be inspected once every 650 flights, but as a result of the mistake, one of the engines completed about 850 flights without being examined.
The officials said there were no safety problems but the Land, Infrastructure and Transport Ministry instructed the airline to take measures to prevent any recurrence.
In February, JAL commissioned ST Aviation Services Co. Pte Ltd. in Singapore to conduct maintenance work on the four-engine Boeing 747. The plane resumed service after the overhaul was completed in April.
It was not until a regular maintenance checkup in November that the engines were discovered to have been attached wrongly.
Reversing the engine locations results in air flow toward the fuselage instead of away from it during reverse thrust. However, it does not create any difference during normal thrust and thus poses no safety problems during flights, the officials said.
They said JAL will revise in-house procedures to ensure that inspections on the planes are conducted after outsourced maintenance work. The current policy only calls for checking documents after the completion of maintenance work.