Link to a 2000 archived page from monkly business regarding mend corroborating the reports above:
http://web.archive.org/web/200012100...ills/mend.html
The guy who wrote the post didn't write things in terms of skill level but rather character level, but since you get (level +1) * 5 in skill, and he says that you quit getting both failures and critical failures at around 19-20 (19 cap being 100, something you might not hit during your time in 19 if you level fast)...