It's a 66 for sure, a -4 I think. Mid to late 20s perhaps newer. It's got the side clamp feet, those were introduced on the 66s in 23 or 24 IIRC.
There is no reason for you to pay money to have that machine cleaned and oiled. It's very easy to do yourself.
The amber coating on the plated parts is old oil that's solidified. It won't hurt anything except the top tension and it can really mess up the tension there.
To clean, fix and adjust the tensions go to TSFR: {
http://www.tfsr.org/publications/tec...machine_manual }
Manuals can be had at the Singer site: {
http://www.singerco.com/accessories/instruction-manuals } Download that and it will tell you all you need to know about cleaning and oiling.
The metal ring under your hand is the belt derailer. You use it to move the belt off the big wheel when you put the machine head down.
That machine would sew pretty good as is, but I'd do a thorough cleaning just to make it look nicer. Oh, use only sewing machine oil and cotton balls on the painted parts.
To date the machine use the serial # at the base of the pillar, letter and all, and go here:
{
http://www.ismacs.net/singer_sewing_...-database.html }
Joe