The exhaust managed to "start" blowing whilst it was with the garage. A hole has appeared on the straight length of pipe towards the back shortly before it turns through 90 degrees and enters the back box - cost to replace this part of the system - £204.87 fitted. Couldn't this plain section of pipe either be wrapped, or if necessary cut out and made good or is this just symptomatic of a complete exhaust system about to go anyway? Would such a repair cause a problem at the next MOT (due July 2000)? (11/99)
From your description it sounds like you just have a pipe blowing at the back box. I'd either go for a trendy aftermarket one or a cheap pattern one. My cheapy cost 60 quid so I won't mind junking it when I decided to replace the lot! (11/99)
I have found that trying to patch up exhausts is a bit like trying to stop the incoming tide demolishing your sandcastle - it works for a bit :-( (11/99)
.. same story on exhaust .. they start to blow ... check clamps for black soot and then replace .. just think of the depreciation money you saved! (11/99)

Thanks for the replies. The concensus of opinion was replace with an after-market exhaust. Once an exhaust's gone, it's gone. However I've ignored this for now...(MX-5 mileage is painfully low at present partly since I've stopped using it for work following malicious damage in the car park - hot cigarette ash on the softtop... - so I'm loathe to spend money on it unless really necessary).

Further investigation showed a 25x4mm hole in the top of the pipe just after the end of the heat shield under the differential. The rest of the system seems fine at present. Visiting Halfords, I found a "Holts Gun Gum Flexiwrap Long-Life Steel Straight Pipe Repair". This is a strip of steel, about 65mm wide with a thin wadding liner which clamps around the pipe with a sort-of hose clip type fixing - cost 4.49 - installed in five minutes (they have other versions for bigger repairs). Importantly it notes "manufactured to meet MOT regulations". So I've fitted one which will hopefully keep the car running for a while. (12/99)