Have you got them really dry inside before replacing them after sealing? If not, it's probably just the same moisture being evaporated & re-condensing. I've only once suffered from moisture on my 147, & that was after replacing a bulb in very damp weather, cured by removing the rear cover, switching main beam & fog lights on & leaving for about ten minutes to get everything really hot. Maybe you've tried that; if so, my apologies, if not may be worth a try before going down the expensive route of headlamp replacement. Another trick I've used on other cars is to stick a sachet of silica gel - the sort of things you get packaged with new cameras, etc - to the back of the covers with double-sided tape & leave it for a week or two to absorb the moisture.
Where are we going & why am I in this handcart?