Make sure the drain vents on the outside are free of debris.
If you split the frame the nut will be rusted to the stud, the studs will unscrew from the window frame though. They probably will need replacing.
If you renew the sealing strip make sure you get exactly the same military type, the ‘new’ replacement strip is a different profile, doesn’t seal and throws the window out of alignment.
I split mine, cleared the crap out, used window sealant below and above the seal. Paying particular attention around the short sealing strips through which the bolts pass. Now water tight..