Word 2003. Hmm, ok. I cannot garantuee it will work then, since I don't use that version anymore for quite some time.
Try the following S&R's (activate wildcards!):
Search for: ([a-z])^13
Replace by ((there is a space after the 1): \1
Search for: ^13([a-z])
Replace by ((there is a space before the 1): \1
That should help with the most. Cases of commas and other tpygraphic symbols are not taken into account. It is possible though, but it might need some trial and error. Word is not always predicatable.
For the processing of the lines with an indent a macro would be needed. That is not done by simple search and replace.