So I took my one buddy out for a drive today and he said my 56-series 'box is on its way out. Now he does work for a gearbox rebuilding center, but how could he know from driving with me? Are there telltales I could listen or feel for?

I was considering an automatic for a replacement to deal with the A15 a bit better (and because I read of a guy who got 17km/liter of fuel with an automatic), and I came across an article on swapping L4N71B gears and overdrive into the 3N71B on a 510 forum. Is this for real? And is it a good idea?

Or should I consider another automatic gearbox and just have an adaptor plate made?

I don't mind modifying the tunnel.