Might help if you actually tell us full story...
What work & mods did you get him to do?
Did it do that straight after he finished job?
Mileage & service history?
Cam/dod lifters shat itself?
Could easily say shoddy service history with engine having blowby issue or something hence oil crud filled manifold or dod lifter let go we don't know actual story/history...
Sorry for the late reply.
Before 'my mate' touched my car, I had already had a VCM 5 cam installed about 4yrs prior with Tie Morel Bar Lifters, Trend Pushrods, Pistons were flycut at the time aswell. Also had a set of Pacemaker Tri Y extractors fitted & custom '4 into 2' 2.5inch/3inch exhaust then Dyno Tuned at which she was pulling 320rkw by that stage. The place that did the engine work didnt think it needed double coil valve springs obviously & eventually one snapped.
When this happened, my mate jumped in said he was going to rip the worked heads off his VE SSV & put them on mine. He pushed & pushed & eventually, I agreed.
He swore black & blue he knew what he was doing & told me that I had no need to worry when I raised any issues that were bothering me.
When we first kicked it over, he was standing right in front of the throttle body & it backfired loud af & literally blew the sunglasses he had on, straight off his head.
I said wtf and again he said it was nothing to worry about.
I had a sick feeling in my gut by then & knew I'd made a big mistake.
When he told me to kick it over again a cpl of days later when we met back at the car, it started but was misfiring & sounded rough af. Thats when I started to tell him to leave it alone. He kept pushing & I had to literally move the commy from there so he would get his f'ing hands off it. I drove it to the closest safe place possible & even though it was a short distance, it obviously did a lot of damage.
Its not oil build up in the manifold. The manifold was clean as a whistle before start up as it was cleaned when we took the old heads off.
Its melted plastic inside.
I'll post more pics tomorrow for you to have a better look