Hi. My name is*****'m a camera repair technician with over 20 years in the business and I'll be glad to help you with your question today.
If you've never taken a lens apart before, I wouldn't recommend it. Even simple disassembly can get complicated fast. There are services available that can do this professionally at a reasonable price and they warranty their work.
The reason I suggested a professional service is the need for specialized tools. Some trim rings need a spanner wrench ti remove while others require a cupped, rubber stopper. These are common tools for a camera technician but not the average person. Do you have the tools necessary to disassemble this lens?
If you haven't done so already, use some alcohol to soften the adhesive under the trim ring. This works well for me and doesn't damage wither the ring or the lens. You sound like you know what you are doing but if you need further assistance, Just Ask.
Hi Michael. Sorry it took so long to get back to you. Have you found something to remove the trim ring yet? I normally use dental picks or other tools I've found that work. If you need to, use more alcohol to loosen the adhesive. It won't hurt the lens s you don't need to go sparingly.