I've killed many a bomb rat in my day, and I've never seen them drop a red gralat. Just a gold gralat or nothing.
Which I'm really not a fan of. Let's face it, it's barely anything given how hard it is to come by a rare spawn. I've long since said that rare spawns should at least have a chance of dropping something special.
I love the concept of rare spawns. But a measly 100 gralats that's not even a 100% drop chance? And now people are saying some are only dropping red gralats? C'mon..
Here's a simple idea: Make rare spawns drop a chest that contains either a random amount of gralats (100-250), a map, or a unique item exclusive to rare spawns (hats, furniture, etc. The rare spawns can share the same drop table, except for one item that would be exclusive to each one: a pet version of the rare spawn. Ie: golden blob pet, bomb rat pet, etc)
If all of that can't be done, then I'd be happy with just the rare spawn pet idea.