Well known retailer....mmmm.....an orange word beginning with the letter H, perhaps?
I haven't lucked in with any bike bits, sadly. Once got lucky with some coilover dampers that were given to me because the lockrings had siezed on the aluminium bodies. Bit of heat and off they came. Sent them off to be serviced and for a hundred, or so, pounds i had a £500 set of dampers.
Best car cheap fix i heard about was one of the hot Volvo turbos. Ran like sh!t if it would even start etc. The owner had been to a well known retailer and even a so called expert with it and nobody could fix it. The owner gave up on it and put it on ebay with no reserve. Chap i knew bought it for a couple of hundred quid, its scrap value, and one short pipe, that cost a quid, like a vacuum pipe or something like that, later he had a 5k street racer!. The ECU was confused with a leak, or a pipe collapsing. Something like that.