I have a Dec 1972 manufactuting date 124G (7 digit serial number and serial number on lens) and I can definately confirm that mine has a metal lever and all smaller knobs like shutter speed and apperture knobs are metal too, just painted black. I know this because of 3 things, they are cold to the touch, I scraped them with a key which made a metal sound and some black paint wore off and shiny metal underneath.
There are however, these plastic parts on mine, the lever washer cover, the shutter lock, the focus knob and battery cover. The rest of the parts on mine are all metal including the film spool knobs.
Out of curiosity, which serial number do you have? Is it a 6 digits or 7 digits serial? Does your lens have a serial number?