'If it has plastic wheels I suspect the OP has the original Tri-ang Railways style 'shorty' Met-Cam unit? With the half-sleeve wheels and open axleboxes? I've seen chipped wheels on these in the (distant) past'
If it is the type described above, you could remove the existing wheels, pop in top hat brass Barings, then fit standard metal wheelsets.
I did this years ago and it improved running no end. Other option, (bit more work), replace bogies.