Wow Tom, I thought I had statistical OCD, but now you're trying to quantitate the un-quantitateable! lol I think that number would be VERY hard to nail down due to too many variables. The mountain itself is the first thing that is going to affect this number. If you have a mountain of lush green pastures with no trees anywhere near where you groom you will obviously stand a much lower chance of tearing a BR tiller wing/cookie catcher off on a tree stump or something. You also run a much lower risk of cracking a windsheild or mirror. If you have no boulders, you're not going to see cracked grousers, worn down tiller tines, or the cutting edge of a blade folded under. Those (to me) are all operator abuse items, but if your mountain is in rough shape the rocks, stumps and trees can take there toll on a cat no matter how carefull or experienced an operator is.
Following the mountain, you have the cat itself. If you're running newer BR/PR's on a really rough mountain with tillers with wings, you can easily end up replacing 2 wings/pivots a year per cat at a cost of $4000. If that same tiller only has cookie catchers and 2 of those get torn off a year, that's only $600. I'm not sure what a PB windsheild costs, but the PR 350 windsheild runs about $4000 (if I remember right), I'm thinking the PB windsheild is less...and they don't seem to crack as easily (I see all kinds of BR's with cracked windsheilds but have never seen a PB with one?!) so I'm thinking a PB fleet would have a lower glass cost.
Lastly, operators. When it comes to cat damage and operator abuse, I don't think years of experience are actually the ONLY variable in this formula...it comes down to the person. Last year, I worked at a larger resort and my shift supervisor was a red neck $%^hole. He had 20 years of experience and broke more stuff in one shift than I broke the entire season because he ran the cats like a red neck #$%hole and didn't have any respect for company property. The year before (my first full time year), I worked as the main groomer for a small eastern resort while the former main groomer (with 3 years experience) went to school and worked 1-2 days a week to relieve me. I worked 85 days of the season, he worked 15....his parts total was $27,000, mine was $350. Again, he was another guy with no respect for company property (or even the finished product) who smashed, crashed and autorotated his way around the mountain. I would actually love to still be working at that mountain, but not everyone can be the Operation Manager's hunting buddy
The production load you place on an operator may also have an effect on the amount of damage a cat incurs, but again this can depend on the person. Some people will rush, do a sloppy job and break stuff in the process, while others will work thru breaks in order to get the job done right. On the flip side, you can give some individuals a normal work load and they will still rush in order to get a longer break. From what I have seen in this business, you can't beat experience production wise, but finding someone experienced and of good character is much harder. Once an operator hits about 5 years of experience there is not a lot of difference between that operator and one who has 20 years experience. Character can make an operator with 2-5 years of experience a much better candidate than a guy with 20 years experience. From my observations, I also think a un-orthodox part of a cat operators hiring formula might be to try and get a look at the candidates personal vehicle. If it's well kept with no visible damage you're likely looking at a better candidate than a guy who has no mirrors and a crunched in quater panel..lol. Maybe ask for a drivers abstract even though they are not running on the road?
So, given all that, I would have to say the number you are searching for depends on your mountain, fleet, and type of individuals you have running your cats, and that every mountain is likely to be a little different. I think all you can do is complile your own data on that one to get an average budget number for your mountain going forward.