I just bought a Mitsubishi Montero 1990 V6 4d and it appears it has the second version crankshaft bolt (the skinny one) and has not been upgraded with the newer bolts that are recommended (I used a mirror to look at the one on the vehicle and it was skinny past the bolt). It has 146000 miles. Do I need to worry about getting the bolt replaced? The vehicle is working well, but it does not have many highway or offroad miles.

Also, will replacing or cleaning the air flow sensor improve the MPG greatly?

Thanks very much from a novice (I have used Pajeros overseas for years but I am not mechanically inclined).