Sorry for length of thread but it gives history

Fiesta 2004 1.4 auto (Very low milage 16k I only do 20 miles a week)

About a month ago out driving and car starts misfiring and wont change gear and amber engine light is on, garage diagnoses leaking core plugs and fixes with new plugs and tigerweld? after admitting having problems with new cores keep popping and leaking

1 week later same problem but no amber engine light, a neighbour has a look and says one of the leads was not seated right, sorted and car drives nice for a few miles then same again and garage says same problem, more tigerweld and no charge (i like my garage man)

Am out again and 2 miles down road same again, same diagnosis same fix and he says he has run it for 2 days and all fixed but i drive it and 2 miles later engine is warm and problem returns. It seems when engine is cold the car drives lovely

Could it be something else? I don't want to be telling my garage guy he is wrong but 3 fixes and still not working. I can just about find the 5-600 if it IS a new head but I cant afford to spend this and the problem still be there

I need advice, can it be something else?

Should i go to a dedicated ford garage and pay for them to diagnose?

Im no expert but try another garage for sure anyway, Ford prices are ludacris.

the core plugs will leak when warm because the engine water system is under pressure, i agree try another garage who know how to fit core plugs and make sure they are fitting the uprated brass core plug from ford.

Update

2nd garage have diagnosed same problem

Tiny leak/steam loss from core plug when engine warm and under load which is soaking the sparks and or leads, they have noted the repairs already done and have advised a stepped solution, step 1 add k-seal to see if that will seal any minute hole or crack around the core plug then a proper road test (not just left ticking over in corner of garage) and then if necessary replace leads and coil pack

Now from other forums i think the use of k-seal will spark a few intakes of breath and would be interested in any response

As a guide for me to allow work to go ahead my ex has had k-seal running in his car since the start of the year following a tiny crack in head gasket and has nothing but praise for it.