Took my GR86 for an oil change at Toyota today and purchased 1L top up oil for £160 (all in) bit expensive but keeps the warranty intact and zero questions.
Listers Lincoln were excellent, emptied the oil right in front of me, further I explained about the RTV sealant issue and the technician was excellent. He knew all about it, and was their lead technician who did all the valve recall timings for the GT86... Anyway, I said "some places I've read are using endoscopes to look in and see if any sealant or debris in the oil" He offered to do it right infront of me. He used the scope and found the sealant and it was all golden on my sump.... no break aways, complete clean lines. Whats better is... I was there for this. He showed me on the endoscope videoscreen everything. Truly excellent.
Further, they disabled my sound generator in the car, and the car sounds WAY better without it. That's before I've even fitted my new exhaust!
Recommend Listers at Lincoln