Não use selador em pedra de engenharia, ele deve ser mecanicamente re-polido se perder o brilho devido à abrasão. Se você tiver sorte, é apenas sujo.
Of course, you cannot apply a sealer to Silestone quartz countertops, so it's just a matter of cleaning it. –countertopspecialty.com
Do not use oil-based soaps for this. Dulling of the shine occurs because of residue left behind on the countertop. Oil-based soaps are often used on porous surfaces because they are designed to soak in, not to be completely removed. Standard dish soap is best. [...]
To remove cooking film from the quartz, spray the space with window cleaner. [...]
Avoid Using More Polish. Quartz countertops are polished within the manufacturing company, using a sealing surface polish. Further polish added to the top will only create excess buildup which will further the dull look.
–How to Polish a Quartz Countertop to Make it Shine, doityourself.com