I am currently writing the chapter ‘O is for Olé’ and thought I’d share this bit, which addresses why “sin problema” has become “no problemo”.
In Spanish, most words carry with them the feminine or masculine gender. For example, a house (“la casa”) is feminine while the sky (“el cielo”) is masculine. These two are classic examples of words that, ending in “a” are feminine while words ending in “o” are masculine.
However, sometimes this is not the case.
The exception to the rule (and there are lots of exceptions to the rule in Spain) can be illustrated precisely by the word “problema”. Although ending in an “a”, this is a masculine word: “el problema”, “un problema”, “los problemas”. So, you can see how “problema” has become “problemo” in the mouths of non-native Spanish speakers.