Sorry to bug people, nothing came up in a search. I'm doing the 4k miles valve adjustment maintenance. Everything is going well, all I need is to take off these two plugs on the left side of the engine. All they have is a long slot, suggesting a simple screwdriver should do the trick, but they seem to be in pretty tight and a screwdriver is not working well. I don't want to put too much force on it for fear of messing up the slots edges. Is there supposed to be a specific tool to do this? Thanks.