Router issues

I have just noticed that my router is not functioning correctly. A 3 mm straight spiral bit or a quarter inch version are producing slots wider than the bit. The bearings are rock solid, no play whatsoever. I noticed a bit of vibration once before and I cleaned out the collet and fixed the issue. This time it hasn’t fixed the issue does anybody have any ideas?I was thinking about replacing the collet with a quality version.

Is the depth stop loose?

No I was using it with a fixed base and the body is solid in the base. I have discovered since posting that it is a collet issue most likely. I am going to buy a genuine makita collet for my generic makita copy. I think it should sort it. Thanks