I use Castrol Power 1 4T 10/40 (Not to be confused with Power 1 4T racing) and have never had a problem with it, I usually change oil and filter every 4-5k miles and only use OEM filters. The one time I was persuaded to try some Q8 stuff I got clutch slip, fortunately I dropped it and changed back to  Castrol within about 50 miles and normal service resumed.
Whatever you use make sure that it is at least JASO MA spec, arguments abound as to whether full synthetic or semi synth is best for big air cooled V twins, Obviously with the Castrol I'm in the semi synth camp.

Motul 7100 20W50.
And the K&N oilfilter which has a hex grip welded on the end of the can so you can fit a 17 mm wrench for tightening and loosening. Very difficult job without, in my view.

Google K&N filter problems mate, been a lot of failures where the hex head is welded on, I always use Hiflo or original fitment they aren't much dearer
Any 10/40 semi synthetic oil which meets required spec

Removal is not the problem but oil leaking out being a danger especially if it gets to the rear tyre

I use Yamalube 10W-40 mineral.
 Change it every year incl filter. HiFlo filters usually...Stage 3 bike.

 First time I changed the oil, I used the Yamalube and it caused clutch slip.
 I deep cleansed the clutch plates with a lheat  gun, basically burning ( carefully) the oil that was already soaked into the friction material. Done gently, it will turn into a puff of blue smoke and the friction material changes from a dark, glossy surface to a dry , lighter colour.  As I had no way of knowing which oil the previous used, it's always going to be a possibility. Oils dont always mix. Thats the difference between clutch slip, and oil incompatibilities.
  Yamalube mineral is perfectly suited to this engine. You need to change it a little more often as the molecular chains, which make it more suited IMO, get broken down more quickly than a synthetic oil does. As this happens, it becomes less effective quite quickly....  As most people dont clock 10K miles a year, I really cant see why they argue the toss about expensive synthetics. There are benefits to both. The trick is using them to their strengths in the right application....