[urq] Average Singing Career of Alternators?

[urquattro at comcast.net]

My junkyard 4k alternator (replacing 3B alternator on port side to accomodate big IC) has begun to sing ever so sweetly after 3-4k miles of use. Given the $10 I paid for it, it has more than paid for itself. The question is, once the bearings (I'm assuming) start to sing, how long do these babies continue to work OK? My cashola is currently going toward resolving my smoking issue, so I'd like to get by with this one as long as possible...

Any BTDT with "singers" appreciated.

-Jon