Hello newbie here.my Fiesta leaks oil it's a 2003 finesse with 1.3 duratec petrol engine.i think it's coming from a poor rocker cover seal and I want to put a new gasket on.however the bolts are in poor shape.i have removed nine of ten bolts the last one roughly above number 2 spark plug is rounded off and I don't know how to get it.i can't drill into it can't grip it anyhow.I wonder if anyone can tell me what will happen if I grind off the bolt head as a last resort.is it likely the cover will come away over the stem of the bolt? Many thanks

Hi can you post a picture of the situation, what kind of a bolt, etc? 

The cover should come off if you remove the head. Careful with the grinder.

 

I think that bolt is 8mm and the position you describe at the back of the cover above no:2 plug will be difficult to access with a grinder. That’s exactly where the gasket tends to perish and leak down the back of the block. If you can get a grinder or something on it, I would try cutting a slot so you may be able to unscrew it with a big meaty screwdriver. Won’t be easy though.

I'd buy something like this 

https://www.amazon.co.uk/Extractor-Stripped-Remover-Extraction-Rounded-Off/dp/B0CZCFLGMB/ref=asc_df_B0CZCFLGMB/?tag=googshopuk-21&linkCode=df0&hvadid=697301774134&hvpos=&hvnetw=g&hvrand=12914411306895542869&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006574&hvtargid=pla-2310310866139&psc=1&mcid=3ce0bf36d7bc35fe934e2cf01c079915&gad_source=1

As soon as you start grinding, hammering etc there's lots of potential for further damage

For the future, avoid using 12-point sockets and invest in a set of 6-sided ones. 

I feel your pain 🥵 Son had a rounded off bolt head, I used my Dremel and cut lovely meaty slot in it, then using my socket screwdriver attachment I was able to break the bolt free.

thanks everyone for generous help with this.funnily enough i bought the exact set of irwins pictured above but whats left of the bolt head falls annoyingly between smallest and second smallest sockets.i also bought a cheapo (and perhaps this is where i am going wrong) version of a dremel.so i now think that i will get onto this tomorrow and first try cutting a slot in for a long screwdriver and,failing that, i shall just grind off the whole bolt-head.probably will end up haing to helicoil the socket but at least once the cover is out of the way i might be able to see what i am doing.Thanks again all you have been great😊

13 hours ago, Duncan2 said:

funnily enough i bought the exact set of irwins pictured above but whats left of the bolt head falls annoyingly between smallest and second smallest sockets.

i also bought a cheapo (and perhaps this is where i am going wrong) version of a dremel.so i now think that i will get onto this tomorrow and first try cutting a slot in for a long screwdriver 

Well that sucks with the bolt head removers 😳

If you cut the slot have you a screwdriver attachment that can be used with a ratchet ?....I can imagine the bolt being very tight, so a screwdriver won't give you much leverage, most decent socket sets will have the screwdriver attachment bit.......Go steady with the little carbon cutting discs, don't stress them but let the disc cut in gradually, stressing discs will just shatter them.