Why do I have less intensity in the bottom of my rear clear lights.?

My car is a Volkswagen MK3 Golf 2L and those are the clear lights. my right clear light at the bottom pannel has less intensity than the rest of all... the problem just began recently. What is the problem and how can I fix it?
I checked background connections, unplugged all, mostly unbuild it... no changes... i am not electrician tho!