I'd suggest upgrading to metal pedals as soon as you can.

I have found the bearings and seals in plastic pedals tend to be rather poor. They're cheap for a reason.

While you will get good service out of them for a while, they will deteriorate quite quickly, and aren't worth the effort of servicing.

Metal pedals, especially if they have a decent, aggressive profile or studs for sole grip, can also bite hard on the shins, so there needs to be some caution there.