Oostrom was successful in his fourth campaign, in the 1984 federal election when he moved to the more affluent riding of Willowdale in North York.
As vice chair of the House of Common's committee responsible for immigration, Oostrom also expressed criticism of what he saw as lax policies towards refugee claimants.
Oostrom returned to the private sector as a consultant before trying to regain his Willowdale seat as a PC Party candidate in the 1993 federal election.
Oostrom attempted another comeback in the 2000 federal election, this time in the suburban 905 riding of Oak Ridges north of Toronto.
In 2003, Oostrom added his voice to those Tories opposing the Progressive Conservative Party's merger with the Canadian Alliance.