o / a

Small function words tend to be unstressed in most languages, and very often have two forms: a longer stressed one and a shorter unstressed one. In Shaetlan the unstressed version of 'of' is o and the unstressed version of 'on' is a:

Wi a bit o luck we'll see dee a Setterday ('With a bit of luck we'll see you on Saturday')

This is neither new, nor slang, nor sloppy language. It started already in Old English: from the 12C 'of' started to be reduced to 'o' in unstressed positions, especially if the following word started with a consonant. The preposition 'on' descends from Proto-Germanic *ana and evolved to an/on in Old English. In unstressed positions it was further reduced to a unless the next word started with a vowel. That's why it is still "ashore" (on+shore) in Modern English.