Moreover Mobil had created a training station in Waikanae which the Bohannas thought would be ideal for them.
But first they had to get a motor spirits licence so they took over a garage on December 1, 1979, on the corner of Elizabeth St and Seddon St until they got the licence in 1981, after a long and frustrating process. This led to them taking over the Mobil site on 24-30 Main Rd, in March that year, where they've been ever since.
It was hard graft especially in the early days with small margins and a mortgage.
"It was a struggle but it's much better now with all the debt paid off," Helen said.
The site has been upgraded at various times for a canopy, CNG and LPG installation, and new tanks (two 50,000 litre tanks).
There have been a few hair-raising moments over the years including when Brent was run over on the forecourt during a petrol drive off.
Brent stood in front of the car, was slammed into, forcing him to take a ride on the bonnet before he hit the ground and had his left ankle driven over, breaking it.
The Bohannas' son Ben gave chase in his own car all the way to Te Horo, cornering the two thieves in a driveway as police arrived.
Another time flames erupted at a car yard next door, not owned by the Bohannas, which led to a spectacular fully involved fire that thankfully didn't affect the station.
They have also been broken into a number of times including once when someone tried to steal a safe that was bolted to the floor.
"They think it was a tow truck which pulled it out — we never got it back — but it had four days takings in it," Helen said.
In 2016 the Bohannas' other son, Martin, and his wife Amanda started the process of buying into the business which enabled Brent to retire.
Helen still plays a key part, especially the accountancy side.
Martin is no stranger to the business having worked there for a long time.
He started pumping petrol at 15, after school, and then after a student exchange he joined the business fulltime.
"People still don't believe I'm the boss and I'm 43," Martin said.
Another generation could be in the business' wings with Ben's son Blake, 15, pumping petrol in the weekends.
Customers are a big part of the enjoyment the family get out of running the business.
"We've got people who have been customers since the day we opened," Helen said.
Martin added, "And we're still a full service station serving on the forecourt all the time."
To mark the 40th staff were treated to Maison 8 restaurant, Mobil helped with some spin and wins, and there are daily lucky draws until Saturday.