Repairing a Nelco Sewing Machine?

My Nelco SZA 2211 needs repair after every project. I'm sewing simple surgical masks. But the wheel that advances the needle slips and spins. When the machine does advance it won't cross a simple bump of elastic in the seam. And the stitches bunch, and gather the fabric. Will a manual give me the information I need to repair this antique? Mine was lost years ago.