rear mech not shifting properly

yes, I know it is rare for me to post about a problem I can't sort out but although I *reckon* I know the cause, just wanna run this past in case some one else has had this.

set up is SLX 9 speed shifter with rear XT long cage mech, Shimano chain and, probably, an LX cassette. None of it is new but judging by the jockey wheel teeth all is in good condition and chain wear is less than 0.75 %.

On two of the middle gears, when shifting down, the chain it will stay on the same cog, shifting down once more the chain will drop 2 cogs to be in correct gear. The mech end stops and gear wire are adjusted correctly.
Playing with the rear gear changer last night I heard a squeak when the cable moved that after oiling the cable in the outer, went away - so the noise was coming from the short outer cable that takes the gear cable from the top tube to the seat stay.

I think the cause of this is too much friction in the cable - also the cable goes through what to me is a rather right curve at the end stop at the front of the top tube.

Anyone had a similar experience?

(I will be fitting new cables when they arrive from Taiwan plus will be shortening them)

Sounds like cable friction at a certain point. New inner and/or outer cable should sort that out indeed.

Forget oil, put grease on the entire inner cable. That greatly reduces friction and has the added bonus of protecting it from rust for a long time.

Raging_Bulls":1elee375 said:

Forget oil, put grease on the entire inner cable. That greatly reduces friction and has the added bonus of protecting it from rust for a long time.

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have been doing this as a matter of routine for a while now, smother the cable then thread into outer, really does make a difference

Possible b tension?

But inclined to agree with the above.