Hi Polly,
I haven't really looked at McCulloch births - Thomas could well be missing from OPRs - just remember that it wasn't compulsory to have your child's birth/baptism registered at the church and quite a lot of couples couldn't afford the fee. Sometimes in a large family you may find all, none or some recorded
It's quite dispiriting when you feel you've hit a brick wall. And certainly at the moment we seem to be stuck. Other than researching every Woodburn family in Ayrshire and finding the connections (and I'm sure that a generation or so before Marion there will be links), I can't think of anything else to suggest.
Marion in 1841 is working and noted on the Census with 2 Woodburn ladies - co-incidence possibly, or did family connections get her the job
Marion is married in 1845 and the OPR reads that she is
from near Bonnihill . There are 2 Woodburn families living near Bonnihill in 1841. Balance of probabilities are that Marion is connected to one or other or both.
If John and Mary Woodburn (nee Brown) died before 1855 there is a good chance there will be no death record - few death records exist -especially if they were not rich.
Another find which may not relate to your Woodburns but I thought worth mentioning considering the date today - 25 th January.
David Woodburn factor of Craigengillan Estate and father of Willie C Woodburn etc (one of the ladies for whom Marion is working for in Kilmarnock) was a friend it seems of none other the the Ayrshire Bard - Rabbie Burns !!
It seems Robert Burns presented his friend David Woodburn with a poem -
http://www.gutenberg.org/files/18500/18500-h/18500-h.htm#XIVGood luck with your research Polly, something may pop up one day
Looby