I changed out the o-ring and block gasket this weekend, with a little over 50,000 miles on my car. The installation was straightforward, but in a few instances I wish I had a third arm, as it would have made reinstalling the hex bolts a bit easier. It took a little less than an hour from start to finish, including gathering tools and putting them away.
For ease of reference, I thought I would include both part numbers in this thread—thanks BOOSTR!
o-ring: 0000-88-C22
metal gasket: N3A1-14-293
I order the parts last Thursday afternoon from my favorite Mazda dealer, and I picked them up Saturday morning. The total cost of both parts, including tax, was $7.44