Grey cell sum of two digits, need tester

[colski]

Thank you. I would like to have to have the steps proven though, so I'm still looking for a tester.

I did this puzzle. some numbers don't go in grey squares. reduce box 1 to symmetric choices of 2 candidates. find where to place 4 and 6 in box 7. proceed until only 3 grey cells remain. I still have two candidates in 2 places of column 4 and 5 places of column 6. the three grey cells in boxes 3,6,9 have 4,2,4 combinations but only one of those seems to work. I don't see a way to resolve that other than trial and error, though.