To avoid stipping the head of the screw, if it's not already done, I usually take a couple of days and soak them really good with a penetrating oil, like WD40 or similar product. I put it on for a day, then go back the next day and put some more on, then wait another day or so after that to give the oil plenty of time to do its magic. The oil will usually work its way in pretty good and loosen it up. When attempting to remove the screw itself, make sure your driver bit is seated completely in the screw and be sure to apply pressure against the screw to avoid slippage. Apply gentle but steady pressure to unscrew it. Doesn't always work, but I've had pretty good luck by taking my time with it rather than rushing it and stripping it out. Once stripped or broken, you may run the risk of causing more damage to the part itself and not just the screw. Just my technique. If all else fails of course, dremels, extractors, and drills work great also. pb blaster,wd-40 etc...spray it and wait...then wait...spray,wait some more...repeat LOL.us DIY/selfers have the time to wait.ive freed alot of rusty bolts etc..by spraying with your fav penetrant and it seems to me that time works well with rusty screws,bolts.if possible a little heat does wonders as well with the above.Key words being "little heat" and "spray and wait" my 2cents..
Ken