How to capture "5, 5 b" (where " b" are optional, but not the space after "5" when " b" absent?

Hi I am using the following regex:


replaced by:

`$1 $4,$5$6``

(where between $1 and $4 there is a \xa0)

I do this in order to correct incorrect or olddated citations and insert \xa0 between the number and the letter:

Joh 1. 3 c → Joh 1,3c

If I remember well I inserted ([^\xa0]) so that It will not go over already done replacements.

Now, I have recently noticed that when the searched pattern is between brackets, this works as a breeze: (Joh 1. 3 c)
However, when the expression is found in a text AND the " c" is missing as in word Joh 1. 3 word, the space following 3 is also selected and then gobbled by the replacement.

Any idea how to avoid selecting the space?