No, I'm not in the IOM, but I have a transcript of the Maughold parish register volumes made by a cousin who lived in Maughold.
The advantage of using LDS films for parish registers, rather than buying a copy of one entry, is that you can build up information about the ancestors and descendants of a particular family for a one-off cost. When you are in the IOM you can use the films at no cost in the Manx Museum library. It is also a good idea to join the FHS (if not already a member), to use their library and have their help while there.
Maughold par reg has William BENSON aged 66, of Ballakilley, buried 29 Apr 1859, which I guess is where you got his birthdate from? Or from the 1851 census?
In the 1851 census he is at Ballakilley aged 58, a farmer of 10 acres, b.Maughold. Wife Esther Benson aged 63 House keeper, b.Lezayre, with unm daur Maria Benson aged 22 employed at home, and grand daur Cathrine Lord aged 9 scholar both b.Maughold.
Maria daur of William Benson & Esther Kneale bapt Maughold 17 Jan 1829.
William Benson & Esther Kneale married 22 Sept 1810 Lezayre [IGI]. On LDS film no.0106727 through their Family History Centres (different film number in the MM).
Cath daur of Thomas Lord & Cath Benson bapt Maughold 6 Oct 1841. Bapt by Revd Mr Holmes at Ramsey Chapel. [In 1842 Register.]
Thomas Lord & Catherine Benson married in Maughold on 27 May 1840
The only other pre-1849 Benson marriage found in the Maughold register was John Corkill & Jemetta Benson on 1 Nov 1845. John a widower. (Jemetta another child of William & Esther's.)
Esther BENSON, 78, Balla Killey, buried Maughold Mar 25 1864.
The 1861 Maughold census has:
1 112 Cott on Ballakilley:
Esther BENSON Head MAR 74 Farmer of 15 acres [born] Lezayre
Maria BENSON Daughter UNM 29 Maughold
John CORLETT Grandson UNM 6 Scholar Maughold
Esther Ann CONNELL Granddaughter UNM 7 Scholar Douglas
Robert CORKILL Servant UNM 15 Farm servant Maughold
1 11 Village of Maughold:
Hugh BENSON Head MAR 35 Iron ore miner Maughold
Margaret BENSON Wife MAR 28 Maughold
Emily BENSON Daughter 3 Maughold
Margaret A BENSON Daughter 1 Maughold
In 1841 (ages rounded):
2 13 68 Bhulushag
William BENSON 45 Farmer Isle of Man
Esther BENSON 50 Isle of Man
William BENSON 20 Shoemaker Isle of Man
Jemetta BENSON 15 Isle of Man
John BENSON 15 Isle of Man
Hugh BENSON 10 Isle of Man
Maria BENSON 10 Isle of Man
No sign of any earlier Bensons (including William's baptism) in Maughold records. Perhaps that Ramsey Chapel entry could indicate Ramsey?
The earliest Benson bapts in the Maughold register were the children of William & Esther, starting with James bapt 15 Sep 1811.
The earliest Benson burials found in Maughold records were
Francis infant Son of ____ BENSON buried Sep 19 1825
William BENSON 6 years buried Jun 10 1848.
1 Nov 1856
Hugh BENSON, Full age, Bachelor, Labourer, Maughold, [father] William Benson, Labourer, and
Margaret KERRUISH, Full age, Spinster, Maughold, [father] John Kerruish, Farmer.
Hugh BENSON 65 yrs., Ramsey, buried Maughold 3 Jul 1891.
Ewan son of William Benson & Esther Kneale bapt Maughold 28 Aug 1825. [Ewan and Hugh forenames interchangeable.]