The only thing I lubricate are the posts, it makes the disconnects work really easy and helps those o-ring last longer. I don't think lube extends the life of the other parts really. When I buy a new (to me) keg I replace everything (including poppets, PRV and posts if they're in poor condition,) and you have to replace the rubber parts periodically no matter what. I don't want any lube or sealant anywhere that might contact beer. (I like foam on my beer and beery flavor in it.) Whatever you lube, use only pure silicone grease. Petroleum products will eat up the o-rings.
(I've never had a leak that lube could fix. I think that indicates deterioration requiring replacement.)
EDIT for that matter, I've never had a leak at all except in a used keg as purchased, they've been perfect after that initial refurbishing.