Is the item you name "light socket" the black thing into which the bulb is fitted and then is twist-locked into the tail light circuit board/housing?

Is yes, then what you need is any such socket - bulb holder - that is the taller size (smaller size is for lower powered bulb) and that has two contacts, not three.

If memory serves, the correct bulb holder will be marked on the back "32cp". They are found in tail lights, wagon and sedan, from 1975 to 1998. The holders in my 1998 S/90 are the same as in my 1988 240.

If you can't find one post, as such, I have bunches in the garage and I'll mail you one at no charge.

Good Luck,