I'm crossing over from the Isuzu board with a Dodge question. Hope someone can help.

The speedo on my '99 Conversion Van stopped working, accompanied by the ABS lights and check engine light. The dealer tells me that the speedo sensor is gone because I didn't change the rear end fluid often enough <img src="/forums/images/graemlins/angry.gif" alt="" />. I've only got 26K on the van and couldn't believe that the manual says to change at 12K. The manual also says to change transmission fluid at 12K (WOW!). Could the dealer be right about the sensor? I've never heard of service intervals that soon and this sounds hokey to me, but with all these interconnected electronics, I don't really know. They also told me that if I towed, I should use synthetics. Is is worth the extra $50? Any similar experience with your tow rigs?

Steve