I need some info on how clean the surface on the block of a 1UZ 98 GS400 should be before I mate the water pump gasket to it.

I scraped the mountains of RTV off and then followed up with a razor blade. However, although it is smooth to the touch, there are still a ton of stains from the old sealant. Must this surface be metal clean or is smooth good enough? If needed, how should I get the stains out and have only bare metal exposed? Sandpaper, what grit? Any other ideas.

Thanks, all.

Pic for reference:










Sidenote: I will be using the OEM WP and metal/rubber gasket instead of RTV; previous owner used non oem WP/T-belt and RTV sealant.

 

Use some fine sandpaper

 

I didn't get any responses in time so I went ahead and used 500 grit wetted with a bit of brake cleaner.