I have a 1999 Silverado z71 i just got and i have noticed when you put it in reverse it has a "clunking" noise coming from the TC. This noise also occurs sometimes when i am going down the road and the truck shifts i will hear it (not as loud as reverse). The TC leaks on the front seal where the rear drive shaft goes in but i know there is fluid in there because i have checked it. I was told by a mechanic that the chains are getting worn out inside (after only 126k miles) he said additive may help. What do you guys think? should i chance additive or get it rebuilt so i don't get stranded when it decides to go south? I have a hard time believing the chains get worn out after 126k miles.