HP Laserjet 4V smudges on second side

[Kitora Mack]

When I print a document front and back, the back side gives me a small smudge down the left hand side. My printer was purchased when the model first came out and I've never had any maintenance done. Probably have around 50,0000 plus runs. Can someone tell me what parts I need to replace.

[redcow]

If you're not gonna send it out to pasture, probably putting in a maintenance kit wouldn't hurt. Here in the states it's C1341-69010. Also i'm thinking a toner vac. or take it outside with an air compressor.