7570 Presser foot leaver..Slow to dropp down

Question

I have a 7570 Phfaff creative. The Presser foot leaver and shaft is slow to drop down or not at all. I have used the machine oil on the shaft and cleaned with a q-tip. It works for a short time and then will go back to the slow drop down or not drop at all. Any ideas?
Thanks from down South..