My husband fixed my machine up like new! He opened it up and cleaned all the dust and lint out (there wasn't much since we had both done that before) and oiled everywhere there was an oil port with sewing machine oil (sewing machine oil does not gum up). He cleaned the old grease off the gears and put new lithium grease on them. He's an auto tech so I guess he knows what the gears and spots to oil look like without a schematic although we did look for one for a month before he messed around with it.
He found the squeak that was driving me nuts!! The big belt that goes up to the hand-wheel was too close to the wheel and it was rubbing on the back of it. He loosened the set screws on the lower shaft and pushed the pulley in a smidgen to adjust the shaft so the belt wouldn't rub at the top.
If you take the belts off to exchange them make sure to use a permanent marker to mark a line across the end of the shaft and pulley so you can align the marks when you put the belt back on. I didn't have to replace my belts, they are like new. Hubby wan't sure so he took them to the sewing tech to buy new ones. The tech said they were like new and didn't need to be replaced. So, back home, after a bit of adjusting to set the timing right DH marked the shafts. Now we're set for next time.