Try:
^(?<Stock>.+)\[(?<Oid>.+)[,](?<Part>.+)\.(?<Description>.+)\]$
If the comma can be a variety of chars, add them between the '[' and ']'.
For example, if it could be comma, semicolon, or colon:
^(?<Stock>.+)\[(?<Oid>.+)[,;:](?<Part>.+)\.(?<Description>.+)\]$