Replicator 2x benchy issue

[Paisleypcdoc]

Hi,
I'm using a Makerbot replicator 2x.
Printing abs at 230'C.

My benchy has a problem with after about layer 15, there is a distinct step as if some layers are missing. Benchy height is bang on though.

Thought it was an issue with z axis wear. Replaced lead screw, nut, motor and driver for z. Rest of machine tightened, cleaned and lubed.

Does the same in makerbot desktop and in s3d.

Any ideas what could cause this? Same place every time.

Thanks.

[S3D-Alex]

Could you post a picture showing the step you are referring to?