Rockshox Monarch Plus RC3 service oil

Hi, I’m wanting to service my Rockshox Monarch Plus RC3 but am unsure what the best oil to use is and also when to get it. Can anyone point me in the right direction?

If you’re referring to the oil in the damper it’s 3wt as stated in the Monarch service manual. Not many places stock it as its not a big seller. 2.5wt is more readily available and can be found in many motorcycle and car retailers if you struggle to find online.
Using 2.5 instead of 3 will have no noticeable difference to the shocks characteristics.