Electrical source issue, motor issue, bearings in motor, worn brushes, ect. My understanding of Silent Drive was to stop the transfer of vibrations created by the single phase power and motors to get a better finish.
If you look at the top of the forum page, Mr. Wells is collecting serial numbers into a chart with the year of manufacture. Go in and find your place and add yours to the list. Just guessing, I would say you are going to be in the mid twenties.(1920's)
It indeed looks like an early one.You can check Mr Wells serial number page(pointing up)showing at the top of the page.Now hopefully the hawkeyed experts will be able to tell you just how original it is. Very nice. I have a 1928 model and as long as I treat it as such, it is a pleasure to use...
Don't use any oil with detergents made for engine use. The detergents can damage the bronze bearing surfaces. Use non detergent single grade oils as suggested by SB or equivalents on the Saybolt chart.
If you have to brush it, get a quart of the thinner for the paint you purchase. Get a few pint and quart mixing cups as well. Use a pint cup to scoop paint from your gallon can to a quart cup. Mix in ten percent thinner to your quart cup. Brush your project with as few brush strokes as possible...
Another useful manual is for the Hercus. Hercus was the Aussie copy of the SB lathe:[url=https://tokentoolroom.com/files/Text%20book%20of%20turning.pdfIt] is a good book to read with the SB- How To Run A Lathe. I found it answered some of the questions that SB mentioned but didn't really explain.