Glad to hear you were able to get it down. On other brands, I've seen a locking strut on a bed platform, but I don't recall ever seeing such a thing on a Sunline. Pretty cool though, the strut had a sleeve on it that popped to the side once the bed was up. You'd have to push it over to center to release so the bed could go down. I kinda wondered if yours had been replaced with those, but it sounds like no.
From your description, I'm not sure if your mattress is on the platform right now? Full strength struts (not tired) are designed to hold up the platform and mattress. If it's just the platform, it will be pretty difficult to push down.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR