HI nick,, yeah the rwc geco will be fine, I use rws co2 target pellets in all my umarex guns pistols and rifles I found to get the best results with those..
As for the Pellgun oil, putting a drop on every other co2 capsule will be just fine and in my opinion is a good idea it's what I have done for years and 'touch wood' I have never had a gun with an airgun with a leaky seal yet, if I'm not going to be using a gun for a few months before storage I also put one drop of Pellgun oil directly onto the seal, this will keep the seal moist while not been used..
Happy shooting.
ATB, Marc..
Some of my favourite guns in. You collection, Umarex Beretta 92fs - Colt Custom 1911 - Walther Lever Action - TM Hi-Capa Custom Build Project - Colt SAA .45 & many more..