Hi Barry, firstly , a posting was done on this site in 2006 from Ivor Clucas researching the same family , through your Robert's younger brother Daniel.
Looking at the fact that when Thomas married Margaret Cowley in 1811 he was a widow , so tried to find his first marriage , so looked for female Clucas who died prior to 1811 , found three possibilities , and one is very interesting , Elinor Clucas nee Quine buried Andreas 7/2/1811, found them marrying Thomas Clucas 18/1/1799 in Onchan. They had the following children that I could find :
1802 William , Ramsey
1804 Thomas , Lezayre
1806 John , Ramsey
1809 Henry , Andreas

So if go on births to the two families , you would expect Thomas to have parents William and Catherine. The hot favourite would be the one ch 6/9/1767 in Malew to William Clucas and Katherine Corkil.
For the same reason Margaret Cowley's parents should be Robert or William and Margaret , so this is half right with what you had , maybe confused because Thomas snr already had son Thomas , but he did call another son William.
What do you think ?
David