Take the motor apart, clean it, clean & repack the bearings (the rear one is a sleeve bearing & the front one is a ball bearing), replace the brushes, & check the commutator for any defects.
Fyi, here's a bit of background on the Model G:
It debuted in January 1961 in "aquamarine green" (or what you call 'blue'). The earlier ones differed from mid- to later ones, because the power nozzle port was on the front of the cleaner and the handle was not equipped with a cord clip; mid- to later ones' ports were on the right side & included the cord clip.
When the motor was upgraded in late 1966 the color was changed to tan. That version was manufactured until 1968.
The model of the power nozzle for both versions was PN-1, but again there were differences from the earlier ones to the later ones & the bumper & cord color was changed to complement the tan color.
The early version of the aquamarine green Model G's PN-1 was equipped with one long cord with plastic hose clips, and the mid- to late ones had two cords: one from the nozzle to the end of the wand, and one that was attached to the hose with rubber straps.
Standard attachments were the upholstery tool/dusting brush small combination tool, the carpet & floor combination tool, and two aluminum wands. Options included: the narrow space cleaner (or crevice tool)-later made standard, the Turbo Tool (earlier) or the Turbo Rug Washer & Polisher (the polisher feature was dropped after a year or so), the white-bristled wall brush, the white-bristled delicate dusting brush, the sprayer, & the vaporizer.
Btw, the Canadian & USA companies began sharing R & D in the 1950s; influencing the development of the Canadian 80s series, which was very similar to the single-lettered models of Electrolux USA, including the Model G. The PN-1 was even exported to Canada (in colors to complement its cleaners).
