Question on lights

[elau]

My high mount brake light is not working so I pulled it out for replacement. Upon close inspection, the bulb appears fine. Why won't it work then? Is there any electrical problem causing that? Other brake lights work fine except one parking light (#5) on the driver side. It is brighter than the passenger side so I pull the light assembly out and compare the two. The bulb on the passenger side is not burning with both filliments but it also appears not broken. So I swab the bulb from the driver side and now the bulb is only burning on one filliment in the passenger side light assembly. The bulb from the passenger side, when put into the driver side light assembly, does not sit tight and won't light up. I check the owner's manual and they are the correct bulb. Anyone has any idea? BTW, it is for my newly accquired '96 W202.