So I have decided to replace my coil as it is getting more and more susceptible to not starting/cutting out when wet and it is also more than a decade old. I found this cheap one on ebay;

http://www.ebay.co.uk/itm/Yamaha-XT6...gAAOSwa~BYPe0G

Are these cheap ones as good as OEM or is it better to pay almost 5 times more for the OEM coil?

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Now have a 2017 S1000XR Sport SE

2006 XT660X - Cat D write off due to someone pulling out on me - Pipewerx carbon fibre exhausts - Snorkel removed and airbox drilled - DNA stage 1 + 2 air filters - Kevs fuel controller mod - Scottoiler V system - Oxford heated grips - HEL braided brake hoses - Wilbers 540 rear shock - Brembo brake pads - AFAM chain and sprockets - Michelin Pilot Street Radial's - Denali DX Xtreme dual intensity spotlights

For that price it's certainly worth a punt. I wouldn't expect to get as long a life span out of it as you have the original unit.