Just a reality check:
I must say that car mechanics I come across are mostly rogues.
and
I must tell that car mechanics I come across are mostly rogues.
Would the second sentence sound unnatural to a native speaker? Would it be different in meaning or tone?
I know that we usually use an object ("tell you") with tell but still, would it be passable as a stand-in for say in this case?
If it would indeed sound strange, would this introduction of an object suffice:
I must tell you that car mechanics I come across are mostly rogues.
Would this be fully analogous to sentence 1?