Replaced 28No. 12v Halogen with GU10 LED's at a hairdressing salon about 4 years ago. Some time passed and customer asked me to replace a couple which began to fade, which I did. Then a few more failed and I replaced. Now 8 have gone dim and need replacing. Any idea what the problem could be. On/Off switches, no sign of damp or other problems. Asked LedHut, who supplied, but no reply. Never had a problem like this and I'm puzzled.