Hi fellow members. Has anyone replaced valve stem seals before in a FS 2 Litre 1999 Mazda GF?

I used CRC Valve Cleaner and now it smokes on start up. CRC refuse to assist, I argued with them stating they need to advertise the risks as well as been keen to advertise the Pro's.

Won't used it again, a product that risks causing your engine to burn oil and smoke, seems Irish!