I think my wife is cheating on me

I've never talked about this before, but I really need the boards advice on what could be a crucial decision. I’ve suspected for some time now that my wife has been cheating on me.

The usual signs… Phone rings but if I answer, the caller hangs up.
My wife has been going out with the girls a lot recently although when I ask their names she always says, “Just some friends from work, you don’t know them.”

I always stay awake to look out for her taxi coming home, but she always walks down the drive. Although I can hear a car driving off, as if she has gotten out of the car round the corner. Why? Maybe she wasn’t in a taxi?

I once picked her cell phone up just to see what time it was and she went berserk and screamed that I should never touch her phone again and why was I checking up on her.

Anyway, I have never approached the subject with my wife I think deep down I just didn’t want to know the truth, but last night she went out again and I decided to really check on her.

I decided I was going to park my motorcycle next to the garage and then hide behind it so I could get a good view of the whole street when she came home. It was at that moment, crouching behind my bike , that I noticed that the valve covers on my engine seemed to be leaking a little oil.

Is this something I can fix myself or should I take it back to the dealer?