One thing to consider, is that the Weimaraner, like all other large, fast developing athletic field dogs, has a life expectancy of about 10 to 12 years. Fully realizing the problems in asking you to consider the situation realistically, you may wish to consider your alternatives should the other stifle require the same surgery. As you know, this dogs lives to run and hunt. That, along with their high level of intelligence would cause me to fully discuss with my vet the probable prognosis if the problem presents itself again.
They are beutiful dogs, and I sincerely hope this can be worked out to his benefit.... when all aspects are considered... Best of luck!