iserith
Magic Wordsmith
I have seen no mention of the 4E rule yet, which (after errata, I believe) had a penalty for failure.
The target DC for Aid Another was 10+(character level)/2. Success gave +2, failure gave -1. A character good at the skill would hit that DC most or all of the time.
5E would require a different target DC. The philosophy behind setting task DCs is different. It would have to be based on the DC of the primary task, say DC-10 or better to successfully aid.
I got the DC wrong, but I mentioned this here.