Overheating or Ram issue? Shutdown cause -128

Hi! Bought few years ago a second hand MBA. Bought it cheaply because it was known to have overheating issues.

Thought it was maybe only a builded up dust inside or the thermal compound has gone to the end of days but now i have fixed/changed.

When the machine came the temps was 70c on idle and when watching for example Youtube it rised to 100c in a heartbeat. Fan controlled manually to 100%.

Sometimes it crashes on boot, sometimes after two minutes and sometimes after 15 minutes. Without the warning or beeps. After (i think) it cools down it boots automatically.

I have then fixed changed:

• SMC/NVRAM reset
• 3xNew termal compounds on original heat sink (less, more and a lot)
• New Heatsink and new compounds
• Changed original 64GB SSD to OWC Aura 128GB (mostly because i bought that before i knew that this MBA would give me so much head ache.)
• Formatted SSD and few times installed fresh macOS to exclude software problems.

But the problem still exist. On log files shutdown cause is everytime -128. Everywhere i have looked for meaning of that shutdown cause is marked possible bad ram but there is always question mark with that code on code charts.

Tried to do AHT and bootable Memtest but MBA crashes before any of those test are complete. No issues with etrecheck.

MBA runs smoothly before crashing.

Any ideas?