The ends and center have an even thinner gold layer, representing only 1/50 of the total weight of the piece. The gold portion of the caps weighs 1/40th of the amount of the total gold/brass cap (not enough to qualify as 'gold-filled', which requires a minimum of 1/20th gold, by weight). The outer part of the band again has the 10 karat rolled gold plate caps. The bracelet is a typical inexpensive period band. a brass core sandwiched between thin sheets of 10 karat gold. The 'R.G.P.' stands for Rolled Gold Plate and is a thinner version of gold-filled. The markings on your watch case simply indicate that the bezel (top of the watch around the crystal) is gold-plated. If you want to post pix, I can probably date the watch within 5-10 years by the case styling. It would do no good because there is no database linking Benrus serial numbers to production date like there is for some brands.

There is no need to open the case to get the serial number from the movement.