Excessive oil residue in air filter housing/some smoking after startup

[HoldMyBeer]

Good afternoon gents, hope you're well.
Tried using search engine here for similar topics, unfortunately not much info.
Guys I'd need your opinion and help on this one.
My CT is 2014 model with 58k miles on a clock. About a week or so I've noticed that there are some blue smoke after initial startup (usually in the evening) coming from exhaust.
Took air filter out to wash it next weekend and changed oil and oil filter and found some excess oil in filter housing.
I had this bike for over 3 years now and done my maintenance on it apart from valve clearances, so some oil residue was always to be found but this time a bit too much.
So like mentioned, changed oil, cleaned air filter, cleaned inside of filter housing and for couple of days there was no dramas.
Then it started again - not every evening, sometimes in the mornings too, so drained about full pint of oil to get oil level in between the 2 marks on inspection glass but problem still persists.
I'll probably drain a bit more and get my wife to sit on bike and level it while inspecting oil level but alway done my oil maintenance on main stand and filled with oil just about to the top mark on inspection glass knowing that some will go to new oil filter - never had problems with blow by residue or even smoking.
Tried looking for smoke while under hard acceleration - none noticed.
Tried looking back for smoke while on hard declaration- none noticed.
One more thing - can this be caused because of incorrect oil viscosity used bearing in mind increased temperatures here in UK for the past month?
Thank you ever so much for any comments regarding this people.
Enjoy the weather and look out for people in cars on their phones!

[Fredz]

Generally, excessive oil in an airbox is indicative of excessive blow-by past the piston rings due to wear.  If it's accompanied by blue smoke that's usually a second indicator.  What sort of air filter is it - K&N, BMC?  How long has the bike had this type of filter?  Ambient temps will no be a cause.  Paper filter elements, unlike washable ones, don't let dust thru.

[HoldMyBeer]

Thanks for that. I hope its not the rings that are failing as this is not the right timing for such expensive service 
I've just wanted to clear that the smoke only comes out upon starting of the engine and this is due to the excessive oil seeping through velocity stack joints in the airbox and into one of the cylinders.
I'll try draining more oil out to see if it helps.
What's the other indicators for worn piston rings?
I've got K&N filter in for the past couple of years. I always thought its doing great job since no spec of dust can be found inside air filter housing 

[Fredz]

Is the bike using oil? That's significant indicator. I spose it's a bit hard to say if you're lowering the level.  It's best to run it at the full mark record consumption over time.

As for K&N and BMC air filters - they are only good for putting in wheelbarrows.  Sure they let more air in, but that's not all.  Some will swear by them but you have the evidence - real sorry about that.

But as I say, run it at the full mark and document usage - it's the only way to verify.

[HoldMyBeer]

I always had oil filled up to the upper limit and noticed no consumption  :187
Has CT got PCV valve? I'll probably be ringing my trusty mechanics to book bike in for inspection... Damn

[Fredz]

For how long then, has it been blowing some blue smoke?  Fairly recently if you had always run it at the full mark?  Your trusty mechanic should ask you for the 'oil consumption per distance travelled' record first thing.  Without that it's guess work.  Visible smoke is only an indicator - the record is the proof.

It has the breather hose to the airbox, no PVC valve.

[HoldMyBeer]

I've first noticed it couple of weeks ago when started bike after work to go back home. Strange I thought. Then next morning when I've started her up all was normal and again, some smoke in the evening. Next day was all OK in morning and evening so haven't panicked and since bike was due for oil change (I change my liquids at half the intervals listed in maintenance schedule) - I thought I'll glance over to see what's what.
So, found oil in air box, changed oil, oil filter, cleaned airbox housing, filled her up and went to work next day. No smoke for couple of days and then again some in the evening.
Came back home, drained a bit of oil and couple of days it was OK.
Fast forward to this morning - hit the start button and some smoke came out.
So my next move is to remove some more of the oil while properly balancing the bike so I don't remove too much and keep an eye on the smoke.
If that persists it's a call to mechanic.
I honestly haven't noticed any oil consumption and never had to fill up in between oil changing services

[Fredz]

   No doubt you'll keeps us posted.  Good luck with it