T5 classic siezing

MY T5 CLASSIC HAS JUST HAD THE ENGINE OUT AND NEW OIL SEALS FITTED. WORK DONE BY FRIEND OF A „FRIEND“. SEEMED TO RUN FINE WHEN RETURNED THEN SUDDENLY SEIZED AFTER 10 MILES. IT WILL RESTART AND RUN AFTER A SHORT WHILE BUT WILL SEIZE AGAIN AFTER APPROX 3 MILES. THE PLUG ALSO CAME OUT LOOKING BLACK AND SOOTY IF THIS IS RELATED. ANY THOUGHTS OR TIPS WOULD BE APPRECIATED

thanks for your suggestions guys, will follow your ideas and keep you posted as to the outcome. once again thank you

hello,

if the engine was runnig well before the fitting of the new oil seal the only things I can thing of is that either a small metallic part was left in the engine case or the piston ring where badly forced, or the piston received a hit that later caused a friction or…
the better thing to do is to observe the seizing marks on the piston and barrel and carefully examin the two. They could be more explicit since the causes can be different

Sounds like the drive side oil seal? does the engine oil smell of petrol?could of put in the wrong way? or came loose,i only use the metal seals held in with JBweld! but Then I tend to think the worst!
Like Curare say’s check it as it wont go away,