Re: 40 years looking for parents of John McLeod, b. 1854 or 1855 in Dyke, Elginshire
www.scotlandspeople.gov.uk - it's a pay-per-view site, but modestly priced. It is the only place to find digital images of almost all original Scottish records of births/baptisms, banns/marriages and deaths (but not burials) and census.
In 1841 there is a family at Sneb, Dyke comprising Donald Ross, 30; Christian Ross, 65; Christian Ross, 25; and Rebecca Ross, 20. In 1851 Rebecca Ross, 27, is with her brother Donald, 37, and sister Christina, 34, at Snab of Moy, parish of Dyke. In 1861 Christina, 44, and Rebecca, 31, are in Forres with John McLeod, 7. If he was 7 in the 1861 census, which was taken on 7 April, so John must have been born between 8 April 1853 and 7 April 1854. That fits perfectly with the baptism on 2 November 1853.
There is a marriage of a Rebeccia Ross to David Winchester in Forres on 13 June 1862. This looks like the same Rebecca. If I were you I would want to see that marriage to confirm the parentage of Rebecca Ross. I would also want to look at the originals of the censuses to see if Rebecca's age really was recorded as 20 in 1841, 27 ten years later and 31 another ten years after that. The 1853 baptism might provide a clue about John McLeod's supposed father Donald McLeod.
I would also want to check the Dyke Kirk Session records to see whether they contain any information about Donald McLeod and Rebecca Ross. For information about this line of enquiry see https://www.rootschat.com/forum/index.php?topic=825881.0
However none of this actually proves that John McLeod, illegitimate son of Donald McLeod and Rebecca Ross, is the one who fathered Alexander McLeod with Agnes Ross.
There is a John McLeod, aged 27, private patient, in Ladysbridge Hospital, near Banff in the 1881 census. I was unable to resist buying a copy of that census, and his place of birth is a bit mangled but could be Snab. The records of Ladysbridge Hospital are in the care of the Grampian Health Board archives in Aberdeen https://www.abdn.ac.uk/special-collections/nhs-grampian-archives-72.php. They should contain enough detail about this John McLeod to confirm whether or not he is 'yours'.
Over to you.