Higgs Boson wrote:

Do they really stand behind the lifetime guarantee?

If you mean their guarantee of satisfaction, not nearly as well as
they did when they were the biggest retailer on planet Earth. The
question is, did they quit honoring that warranty because they're no
longer the biggest, or are they no longer the biggest because they
quit honoring that warranty?

I don't believe Sears ever warranted power tools for life, just most
hand Craftsman tools, but excepted from that lifetime warranty are
Craftsman measuring tools (calipers, torque wrenches) and cutting
tools (saw blades, drill bits, router bits).

My saw is so old I no longer have the paperwork. I brought it out the
other day and it would hardly cut. I don't think it's the blade; I
either had it sharpened or I replaced it not that long ago. It roars
a lot, but doesn't cut much.

Could it be the motor brushes?

If the Sears part number is still legible, try Sears.com since they
have service information for quite a few of their products and other
brands.