Engine turning is unrelated to clutch hydraulics (only brakes, vacuum boost). You mentioned new master, slave in 1990. They are now 34 years old.
Have you been refreshing the hydraulic fluid every 24 months all these years? If not, its normal, cheap insurance, and relatively easy to refresh master, slave, and hose.
If there's something wrong inside the bell housing, you'll be dropping the transmission, but start with the easy stuff.
Also, 34 year old flex lines to the brakes are way past their expiration date.
Have you been refreshing the hydraulic fluid every 24 months all these years? If not, its normal, cheap insurance, and relatively easy to refresh master, slave, and hose.
If there's something wrong inside the bell housing, you'll be dropping the transmission, but start with the easy stuff.
Also, 34 year old flex lines to the brakes are way past their expiration date.