Rocker cover oil filler leak

[Beebop]

Following on from this https://wilddog.net.za/forum/index.php?topic=254379.msg4570924;topicseen#new
I have a more complex issue:

I stripped the original coating off my rocker covers as the one had been damaged and repaired
with filler which didnt look that great. Once they were down to metal, I polished them and they looked good,
but magnesium doesnt hold the shine, so I painted them satin black, which looks good, but....... the original
coating is very thick, probably up to 1,5mm in places. Now that its all off, I find that the oil filler ring does not
snap in as tightly, and leaks. I have replaced the plastic parts and O-rings with no joy.
Any suggestions on how to resolve this ?

 

[Welsh]

 

[Beebop]

 

[Gerard]

 

[Chrisl]

 

[jaybiker]

 

[SabreF86]

 

[Welsh]

 

[Ramius]