I purchased one for my 298 Vista (twin Volvo Pentas) and I believe it was from Volvo Penta themselves. Don't worry though, the warranty companies will be crawling out of the woodwork before too long to offer their services. Not cheap, but it gives you a piece of mind. I would talk to your dealer because I tried to utilize mine for my trim senders (which were under the warranty) and I never was able to get someone to fix them. My dealer had gone out of business and no one else cared.
P.S. I just read Cap'n Morgan's post while previewing this one and he is right on the money with regard to the hassle. However, you better have a big cookie jar if something major happens. I would still recommend one for the big hit.
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Current Boat: 2000 Four Winns 298 Vista
Previous Boat: 2000 Carver 406MY