etiquette - Is it ever appropriate to correct a non-native teacher's English?

Four of my Japanese teachers are, as you would expect, Japanese, and they all speak English fluently. But now and then, there will of course be slip ups: I often see small grammatical errors in one sensei's handouts. They don't affect the quality of the communication, but is it appropriate to point out these errors to the sensei?

I know that if I were in Japan, I would always want for native speakers to correct me if I made a mistake; more so in the written form. However, this particular sensei has been at my uni for something like 20 years, and her English is perfect in all other regards; I wonder if it wouldn't be a little insulting to point out otherwise negligible written/spoken errors. Nonetheless, I'd like to know what some teachers think.

EDIT: When I say my sensei's English is perfect, I mean that she is able to communicate effectively, not that her speech or writing are free from grammatical errors. Like any non-native speaker who hasn't learned from a very young age, she will sometimes say or write things that sound jarring in English grammar.