at the time that they were overhauling these engines they didn't have the knowledge then as anyone working on them at the time knew. lots of engines off overhaul at east kilbride that didn't make it to airtest , so where now would they find the expertise now ? Will be from the books i guess. Recall in the early 80's lots of issues mainly with the 100 series , recall the guys at yeovilton struggling to fulfil the contract due to engine problems. Seem to recall them trying to take it away from RR but wasn't allowed. Must be plenty of other engine guys recall this time !