Again, thanks to Martin Lavender for sharing his experience!
"After the replacement small reduction belt the printer worked well except that at one point the document lines were jagged across a two inch section of the document. It turns out that there was some dirt/oil on the encoder strip but this has now been cleaned with a damp tissue and dried thoroughly and very carefully not to cut yourself! This has resolved the problem."
"After the replacement small reduction belt the printer worked well except that at one point the document lines were jagged across a two inch section of the document. It turns out that there was some dirt/oil on the encoder strip but this has now been cleaned with a damp tissue and dried thoroughly and very carefully not to cut yourself! This has resolved the problem."