Hallo Richard ,
You may have this information already .... if not ,
the late Lord Strathspey's '' A History of Clan Grant '', may be of help . I have lent out my copy , but if I remember correctly , there is a small piece on the 5th Earl.
thePeerage.com has this .......
Sir Lewis Alexander Ogilvie-Grant, 5th Earl of Seafield was born in 1767.1 He was the son of Sir James Grant of Grant, 8th Bt. and Jean Duff.1 He died in 1840.1
Sir Lewis Alexander Ogilvie-Grant, 5th Earl of Seafield gained the title of 5th Earl of Seafield. He succeeded to the title of 9th Baronet Colquhoun, of Luss in 1811.
Citations [S75] Lord Strathspey, A History of Clan Grant (U.K.: Phillimore, 1983), page 108. Hereinafter cited as History of Clan Grant. http://www.thepeerage.com/p18880.htm
Hope this helps