My 18K miles SEL's trunk lid strut has weakened. Up until recently, the truck lid would pop fully open immediately and hold on the level or on an incline. I was impressed with its function.
While on a recent road trip, I bumped my head while reaching in for my luggage and noticed that the lid was about 4 inches from being fully open. When I closed it to take a load into the room and then returned, it would open to only about 6 inches from fully open. When I pushed the lid up manually, however, it would hold in that position. Later, when I parked in one lot on a not too steep nose up incline, I noted that the trunk lid would only open about half way, and that it would not stay open when I pushed it up - I had to hold it open with one hand to get it above my eye level.
I noted this to the dealer when I got my oil changed last and the tech opened it up once and left it saying it worked fine, no defect, no leak down. I told the service manager that it would often open fine after being left for a time unopened, but when closed and opened again, it would not open fully and I mentioned the incline droop. The manager said that if the part goes back to Ford and they find it okay, they will deny the claim. She would order the part anyway though and call me when it is in. She just called me, the part's in and it will be installed tomorrow morning. Nice work Sandy at The Ford Store.
You might want to keep an eye on your Focus trunk lid. BTW, there are helper springs on each side and these are the primary opening force for the trunk lid, assisted by the single strut. There are two types of springs for the Focus, a stronger spring if you have a spoiler installed. I'm thinking that if this happens again, I might just get the stronger springs.