The labour largely depends upon where the oil is leaking at the gearbox end of the engine. If it's crank seal then it's engine out, these are rare however. It's more likely to be distributer or cam cover leaking at that end at the back.
Leaking from the oil pump gasket is common, the oil pump bolts work loose and the gasket then lets go. It's a sump off, cambelt off, oil pump off job to do. I always reccomend nipping these bolts up when changing a cambelt.
I would say 18 hours would be a worst case estimate for someone familiar with the cars and kitted up. This should cover dropping & refitting the engine and changing oil pump gasket while out.
I've heard good reports of Japex at Kings Langley but no personal experience.
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If at first you don't suck seed, try drier grain.