wow, that's some really nice and serious weathering! makes Demi's paintjob look fresh and new!
regarding grease and oil - you want it to look slightly shiny, so there are two things to consider:
- using "vallejo model color smoke" - it's slightly glossy (but in a greasy way) with small particles within, so it definitely is a good choice for such weathering. it's perfect for sooty exhausts - if you need you may flatten it with varnish, but I think it won't be necessary
- adding A LITTLE scenic water effect to your paint - it's sometimes used to create mud, but a very thin layer (slightly translucent) will look like oil stains
Adding a glowing weapon could be a very nice touch, but if you make a mistake you can easily spoil such a great paintjob. So unless you know you will do it right, practise on a different model first.
Really nice paintjob here!