Gogic and new Scotland call-up Lennon Miller menaced in both field earlier than the interval, however the second half delivered fewer alternatives and extra chaos.
Boyd-Munce was carried off after a sickening aerial conflict. Ellery Balcombe worn out team-mate Liam Gordon and Olusanya as he raced out to clear.
Slattery, nevertheless, offered one other telling second.
Latching on to a ricocheted Tony Watt knockdown, he flashed, first time, low into the web from 18 yards.
Olusanya continued to profession across the Motherwell half and, already on a yellow card, he thundered into Dan Casey. Referee Grant Irvine brandished one other.
In a chaotic endgame, 14 minutes of further time had been performed, however Motherwell couldn’t stun their depleted friends.
Gogic had the perfect opening within the dying embers, arrowing a header into the Davie Cooper Stand from a nook.
Slattery’s targets maintain Motherwell three factors away from St Mirren, although they fall one behind sixth-placed Hearts within the quest to achieve the highest half.
