Just add “any” cargo selection. Means “appropriate to the type of car”.
For example, coal and iron both goes into hopper. So why not let a hypothetical “manager” of she station decide, what can be load at this time?
Of course, there should be a tanker truck to deliver oil by roads, but since there is barrels – I’d stuck with “any available” selection by default.
So, selection for horse cart would be like that:
And for railroad hopper wagon:
And that’s all.