Many thousands every year?
Suuuuure.
Though you conveniently "forgot" to include the qualifier "for one reason or other" the fact is far more Priests leave
for one reason or another than are added to the rolls.
Using a single statistic "Priests who leave to marry" we can see a decline in active Priests of approximately 1,700 per year.
PRIESTS WHO LEAVE TO MARRY
Factor in deaths, retirement, for reasons of faith, "kicked out", etc., and it is rather simple to say "thousands" leave each year.
I await your documented rebuttal.