www.flat6innovations.com, a board sponsor. You will get a professionally re-engineered M96 motor, that will not implode. However, you will not get it for $4-5k as your post specifies. If you buy a used motor off eBay or a dismantler, you're going to face the same problem or someone will, if you sell it after replacement.
Sorry to hear of your troubles and the warranty company jumping ship on you. They are a bunch of crooks, if you want my opinion. Better to just stick a thou or two in an account annually and self-insure rather than give your money to the profiteers.