I have never had any residual grease that was difficult to clean. Slightly damp fouling, that is given a chance, will dry and harden - thus, guys who shoot the accuracy games, with 5 or 10 minutes
between shots, clean after every shot. We don't and we clean with water. I clean my BP ctg. rifle(s) with plain water and it works perfectly.
I think folks envision problems where non exist, or perhaps just overthink many situations where there is a simple fix.
As to Petroleum and black powder fouling, the two do not mix., as in Lee's Liquid Alox is not a good BP lube: try it. Petroleum products, like normal Hoppes #9, or Butches Bore Shine will not
dissolve BP fouling either - but water does that, without an needed additional chemicals.
Vaseline, might be be a petroleum "product", but like many synthesized petroleum products, it's chemistry has been changed. When mixed by way of heat and with beeswax, then subject to
intense heat of the fire from burning powder, it becomes one of the best black powder lubricants I have seen. For me, it has been the equal to Lyman's BP Gold and Steven Paul Garbe's SPG lube
that many BP ctg. rifle shooters use today. I have used it as a bullet lube in grooved lubricated bullets as well as a wipe on a paper patched bullet, with a slug of it beneath that PP bullet as a
lube ball. 60:40 is my mix and it continues to work well for me.