1992 SL500 - Belt/Tensioner noise?

Upon accelerating there is a dreaded squealing noise comoing from the front portion of the engine. I have read on this forum not to lubricate the belts for it may cause futher damage. Is this true? Also, I've read a little bit about the Tensioner issues as well. Could anyone help me with a possible cause of this horrible noise??? Please?

there are a couple of things, either the tensioner is at it max adjustment and is allowing the belt to slip, or the belt is cracked causing excessive slack in the belt allowing it to slip, look at the belt does it have cracks? also look at the adjusting rod, is the bolt inside visible, or is it flush with the bottom of the adjuster, if it is flush, this is a good sign that the tensioner is at it's max adjustment and should be replaced

Thanks a million...

The belt looks just fine, clean, no cracks. I'm still trying to learn more and more about this car. I know this sounds academic but where is the adjusting rod and if the tensioner needs to be replaced, what would be a resonable dollar amount I can expect? Again, sorry for my ignorance.... any help is really appreciated