Only Cub Cadets - Crankcase seal?

Hello to all. I own a LT2180 with a briggs and stratton vanguard motor. Bought it used a few years back and it's been fairly reliable, only has a little over 400 hrs. Last week my wife was mowing while I was at work (cause she's IMPATIENT) and called me to let me know it was messed up, was dying on her, wouldn't run right but she was able to get it back to the house (we have 3 acres) and parked it. I got home and the first thing I noticed was a flat tire, which she wasn't aware of but apparently the two incidents aren't related. So, I fixed the tire Saturday, installed it, started the mower so I could finish mowing and it died after a minute or so, I didn't get two feet. Then it would not start. I pulled the plugs to see if they were wet, nothing there (although they are gray instead of the normal tan?). Pulled the aircleaner to have a look, had everything off and started it. Seemed to run OK but I was getting a good amount of oil out of the crankcase vent which as I understand it is not good. After a few minutes that kind of stopped, but I think it did so because the crankcase seal blew, it started dripping oil everywhere from behind the pto clutch. Thankfully this happened while it was parked, if it had blown while I was mowing I'd have a trashed engine ( I checked the oil when I was looking at the carb, about halfway between full and add) SO, seal replacement seems pretty straightforward, but what in anyones opinion would be the underlying issue? It seems I have an undue amount of crankcase pressure, kind of reluctant to replace the seal if it's going to blow again. Or it could be one of those ' it failed just because' issues, but I want to cover everything while it's down if possible. All knowledge is appreciated, thanks.