+Vintage Misery They kinds explain it in the show too, I forgot the episode but they say that his armor locked on him for a day and he couldn't get enough oxygen which gave him some brain damage.
They've already started, RvB Reconstruction, there's about 8 or 9 (I don't know, so I'm probably wrong) episodes. Reconstruction is season 6, in case you're wondering.
People have mentioned how Caboose and Donut act a lot differently here compared to later, but honestly Grif is just as different going back. He seemed to have some degree of care for his job here, like immediately telling Simmons to get the Warthog upon seeing Donut had the flag, and early on generally seems to show more respect to Sarge. It’s interesting to go back to this early era for sure.