Cleaning extender

I have to as a technical cleaning question. I have a kenko 1.4 extender, I have used it several times and never noticed until I did a whit back drop shot that it appeared to have a blemish that was showing in my pics.

I removed the extender and shot with out it and confirmed he blemish is being produced by the extender. I have tried several attempt of just cleaning it off with the cloth and have had no luck. What should I do? I am unsure of any other way to clean it other than the front and rear glass. Any help appreciated.

Do you see something in the optical path that is large? If not, you just have a dirty sensor.

It isnt the sensor. I take the extender off and the blemish is not visible. That is how I came to the deduction that it was the extender. I take it off and the pics are clear I put it on and the image has a small spider shaped blemish almost to wards the center top of the photo. It is in the same place once the extender is connected.

Shine a flashlight through the extender off the camera and see if there is anything obstructing.

ok going to go and try that right now...
thanks

I tried that and I cant see anything. I cleaned the extender with the cloth and put it back on and snapped a few shots where my clock is with a white back ground. The blemish is still there but not visible to my eye even with the flash light.

I took some other pics and now believe it is the camera itself. Not to sure on how to clean that out but I guess I will be learning. I mean I can always crop the pic and take that marking out since it is so close to the middle edge of the pictures but I really would prefer if I didnt have to do that and the picture was clear and clean.

Turned out it wasnt the exteder and it was the sensor. I looked up how to clean the baby and the pics are now clear.
Thanks for the replies guys I really appreciate the help.

Rick