On the S and CH, those people who come from eastern provinces near Vietnam borders e.g SvayRieng tend to pronounce words starting with Ch into S.
It's probably an influence from the Viet that developed this accent. So a person from Svay Rieng province would probably say "Baan Seo" but that's a vietnamese word, so I can't say much on that word.
Chnum (year), S.R people might say S'num, and that's one I think of at the moment.
We have a lot of different accents in Kampuchea, that's why sometimes we can tell what province the person come from on the way speak and the words used.
Noyume - haha, probably your father had khmer friends from eastern cambodia, or khmer yuan friends in his village back in his time. Oh yeah, it's 6 bucks. I know it's crazy. you guys are lucky =/. we have 1 size too.
That old language you mention is probably Sanskrit. Even the French has the word Mae for Mother. And Pa for father.
About the word Bpa/baa/paa, in Kampuchea, the urban areas use the word "Pa" which is possibly influence from the French's "Papa/Pa" or Teochiu/Mandarin.
The proper word for father in Khmer would be Ou-bpook, or shortened to Bpook/Ou, depending. Same for Mae. Now, most people says Mak, Bpa, Mak, Bpa.
In Thailand, it is a similar case. The Thais use "Por" as a proper word for father.
"Dragon" and "Rabbit" would be pronounced "neak" and "tonsaay" in normal Khmer vocabulary.
"Roong" and "Thors" in Khmer would be used for the 12 animal cycle. The 12 Animal Cycle is probably influenced from the Chinese long time ago in the time of Angkor.
"New", the Thai probably borrowed
and shortened "Thmey" to "Mey".
Fixing the car, I never seen that "Sua". I only heard of "ភ្ជាប" P'jeab.
"Heng" or "Luck", I only know "Somnaang".
And about the Gasoline, if you say that this word "xang" is a new vietnamese word, how can you say that Khmer borrow from Vietnamese? Don't say that without knowing Khmer language. It sounds something like "Sung" and "Sang" mixed. It's hard to say in this English script. ប្រេងសាំង or សាំង would be "brangsang", or shortened to "sang".
And about the "purse", "ka-pop", obviously Khmer did not borrow that from Viet, it's from the French in that colonist period.
I'm a native Khmer speaker, and I know much about my language. I don't think foreigners know a damn about my language to even talk about it. =/