is there such a thing? And is it possible to replace it without having to replace the whole tensioner?

Mine squeaks (and it's not the belt)

 

The bearing on the serpentine belt tensioner is not sold separately. You'll need to change out the whole thing and it is an easy job. It's about $170 at the dealer or you can get on at rockauto.com for about $70. Dont wait on this. Mine stranded me when the bearing siezed and shredded the belt too.

 

i'm assuming it's as simple as taking off the belt, unbolting the tensioner arm, put the new one on, and put the belt back?


mine isn't annoyingly loud or anything... but i can hear it... sorta like a very soft whining sound. It started off a bit louder squeal, after some belt dressing... it got a little bit better, and then after spraying the bearing down... it turned into a very soft whine.

 

It is as easy as this:
1)Release the belt tension by putting a socket on the bolt in the middle of the tensioner pulley and swinging it enough to slip the belt off.
2)Take off the upper and then middle cam gear covers to expose the tensioner mounts. These are all allen key bolts.
3)Unbolt the 3 tensioner bolts and put the new part on.
4) Reverse the above and you're done.

You did the right thing by spraying the bearing in the meantime. Just dont use WD40, make sure it is a penetrating lube. WD40 could do more harm by rinsing all the remaining grease out.

 

On an SC400, you can buy just the pulley w/bearing already installed - Dayco makes them. That said, it would probably be a good idea to just go ahead and replace the entire unit.