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.