Clean the pivot as best you can (shoot it with WD40, then rinse with hot water), then lube it.
I would add a thumb stud by drilling a hole through the blade with a 3/32" carbide drill bit, and installing a screw-in thumb stud from Knifekits.com.
Even if the thumb stud doesn't allow you to open the knife one-handed, the stud can give you something to grab onto and pull on when opening the knife using both hands.