S70 Timing belt Tentioner

I have a 98 S70. I had the timing belt done at 79K miles in July 03 at a Volvo Dealer. At the time I was never told that changing the timing belt tentioner could save me lot of headache down the road. I recognize that Volvo does not recommend this, however I spoke to a head mechanic at a different Volvo dealer and he said he usually recommends it to customers. About a month ago at about 89K mile the tentioner jammed on me leaving me with a $3600 bill for a new engine head. Obviously the dealer is refusing to take any responsibility. I am putting this out to everyone on this board to get some feedback. I welcome any advice as to how to recoup some of my losses and/or hear from anyone who has gone through the same experience.