The presser foot shaft is sticking-takes several seconds for the foot to lower. Looking up into the shafte, it looks like there is dried glue which I am thinking is grease. Machine is very clean otherwise. Cleaning off that residue & appling sewing mane oil very lightly with a q-tip it worked great then a week later was sticking. Suspect dried lubricant or is there a bushing that could be broken? Cannot see how to remove the face plate to look inside. Thanks, flo