before actually asking for the letter...

[candycrava]

There's a professor that I think may write me a letter, but I have not seen him in over a year. Should I ask him to review my SOP before asking him to write a letter of rec, so that we get reacquainted first, or should I just go out and ask him?

[Usmivka]

I'd think a meeting might be in order first...chat, remind him who you are, give a CV and talk about your goals and where you are applying, and most importantly what you thing he can speak to in your letter of rec.

[amlobo]

If you are in physical proximity, meet with him. If not, drop him an email or a call to explain your plans. I contacted a professor I haven't seen in 6 years to write a letter for me, and I just sent him a lengthy email updating him on my life and plans... and then asked if he would write a letter at the end of the email and offered to send my SOP, previous papers from his class, etc. He was more than happy to write a letter and has offered to go over whatever documents I'd like help with. I was pleasantly surprised that he both remembered me and is so enthusiastic about helping me with applications, 6 years after graduating. So, I would say that one communication of some sort "catching him up" is sufficient, and you wouldn't need to contact him under the guise of asking for help on the SOP. He will probably assume that you want a letter of rec if you do that, anyway