Make sure there's no cracks and that the bulbs are sealing correctly. Otherwise, it's pretty common on Gen 1. It used a rubber butyl sealer that softens with heat. It's usually fine if applied correctly. It may be possible to reseal it by putting it in the over for 10 minutes at 210F and then pressing it together. If it doesn't budge, try 5 increments. Remove the clear adjusters first! 1/8th turn and pull. Get it to room temp before removing those as the adjuster sockets can crack. Don't put it on the wire racks. Use a cookie tray. Don't put it too close to the heating element. Caulk or tape over the lens/housing seal is a poor but less risky alternative
Gen 2 has permaseal, which sets permanently. The above does not apply to them. They're usually pretty well sealed as long as nothing is left open