@Seminole81 what voltage are you getting down the live wire to the bulb?, if you can try to get the probe on the mutimeter onto the pin in the middle of the bulb holder as thats the live and the metal surround is the earth, it could be the holder itself or the bulb may not be contacting properly inside the holder, if you have a little pick or screwdriver you can bend the live pin up a bit which should give a better contact to the bulb or get a pair of pliers and squeeze the body of the holder so that the bulb is fitting really tight into it, i'm not the best with electrics tbh but know basic stuff.
@david1972 not sure if itl be a fuse as i think the rear sidelights are on the same fuse as the front, there will be a fuse for each side, i'm not sure how the front side lights are wired up on your car as i've never worked on one but could it be that the previous owner had a problem with them and wired them in together and now theres a fault with the wiring, its kinda strange how both are not working at the same time unless both bulbs are faulty but i'm assuming that you've already checked them