Bought a used Beretta Cougar with Trijicons. Noticed the rear sight has "H3 97" on the side which I took to mean that the tritium (H3) in the sight was from 1997. Half-life of tritium is about 12 years. Sights are noticeably less bright than some I had put on my XD-40 last year. Can the tritium inserts be replaced or do you have to get the whole front/rear sights replaced completely?