Teacher, is this sentence OK?
We received your letter of May 1, 2012. We see that there is a typo on page 2 of your letter regarding the date of the issue of the brochure. The date of the issue is January 15, 2012, not January 15, 2011.
The "is" is okay, especially when combined with "we see" instead of "we saw." It's still there. But is there a point in writing such a letter?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.