Like point-producers in Boston in the 1960s to 1990s, goalies in Montreal from the 1970s to early-1990s often looked very average when they left town. If you were an NHL-level goalie there was no better place to be than Montreal during that (extended) era.
Rick Wamsley
Shared a Jennings trophy in Montreal (1981-82 Habs were the #1 defensive club of the entire 1980s)... was average otherwise. To be fair, he did have a couple of good seasons in St. Louis, but by the late-80s he was already a sieve.
Denis Herron
A good goalie with a fine career in Pittsburgh, but came to Montreal and in two out of three seasons had the #1 save percentage in the NHL, including a staggering .911 in 1981-82 (albeit as a back-up to Wamsley), which must "adjust" to about a .950 today. Then Montreal sent him back to Pittsburgh where he had three seasons with around a 4.80 GAA and an .865 save percentage.
Bunny Larocque
As mentioned above...
Brian Hayward
An .864 with a 4.28 GAA after four seasons with a not-bad Winnipeg club in the early/mid-1980s. Comes to Montreal and immediately has the #1 GAA in the NHL, matching Patrik Roy's stats for two seasons in a row.
Even Patrick Roy never had statistically-dominant seasons again after leaving Montreal. (Fortunately, he made up for it in other ways.)