These screws can be a pain, especially if you dive in there without suitable preparation. This is what they looked like when new:

 

 

They're generally a Torx T25 tool fitment, and they're mostly a bit or a lot rusty, and almost always have grit and mud in the head recess.  If you do nothing about the latter before attempting to undo them, the tool tends to slip, or you can rip up the head and make life more difficult than it ought to be.

 

I tend to replace any that are badly corroded and like using this fella on ebay for such things.

 

But before you can replace, you need to get them out. Things like an old toothbrush or a small wire brush can help, but both will struggle to get deep into the head recess where the grit and dirt are really in the way of the tool getting good purchase.

 

So use a little pick tool instead. I tried this for the first time a week or two back and it works beautifully, getting right to the bottom of the recess, and into all the corners nicely. Anything similarly pointy should do, but these sets are available very cheaply on ebay/Amazon/anywhere. Suddenly the torx bit goes in about 2mm further and just releases the screw easily.  

 

Bloody obvious strategy in hindsight, but may be handy for anyone who has successfully evaded the bloody obvious to date. 

 

 

 

 

Edited 21 March, 20215 yr by Wino

I have also recently bought a pick set like yours but a long handled one, before I was using a sheet metal scribe to clear out the recesses in those fasteners or anything similar, it does indeed make a big difference and having a choice of dedicated pick tools has made an even bigger difference, I dont know how I lived without them for so long, same goes for the plastic trim removal lever tool sets.