I have a 2004 summit been a badass sled, how often do the crank seals need done, I believe mine are allowing air to get sucked by, I have put 4k on this sled, but overall it has 9k on the chasis. again a lot of work done by Felkers of Denver to it and keep everything running great, also, should I do the bearings while I have it tore down, any tips on changing these out, How do I know if I need to do the center seals. (I am aware I would have to have a shop do that), any info would be great, I have never had to crack this sled and don't know what to expect. thanks.