Oil For Tt600

Hey all, hope you are all keeping safe and well?
Whilst in lockdown I thought I would take some time to do the servicing jobs that I didnt get to do over the winter.

So far I’ve done a brake fluid change and a coolant change next job is the oil and filter. Now in my handbook it says 15w50 either semi or fully synthetic but everywhere i go to buy the oil online, whether i put in my Reg or make model and year it tries selling me 10w40. Surely thats too thin and as the engine gets warmer, its not going to give the lubrication it needs as it gets thinner with heat?
I checked the oil and its still really clean, lovely amber colour on the dipstick, but i think its too thin as the gearbox seems a bit clunky when its up to operating temperature, but is fine before then. I didn’t do the last change so i don’t know whats in there. Whats the general consensus on this?

 

I know its a pretty standard oil, i used it in my old Bandit 12, but that was the recommended grade. I know the bike is an old bike now, but i dont want to wear stuff out quicker than it should. Its only got 20k miles on it!

 

Im thinking the same but i was just curious in case someone from Triumph was on here that could give me a definite yes the 10/40 is fine or not.
Also having just read through the K&N oil filter failure sticky, i was going to do this urgently as I have one on the TT and i dont want mine going pop!

 

Thats not bad. Ive just found a shop on flea bay doing the same for £36.95 including a free HiFlo filter with free postage so either or really.

 

My manual says Castrol but i dont think the brand of oil matters so much now its out of warranty, as much as the grade. I was thinking of either the Motul 5100 or the Rock Oil Guardian Sigma. Both are about the same price and have similar viscosity at temperature.