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No...no...no. Not now, not ever. Took my 65 to 118K before putting her to bed for a rest. As long as you keep up with servicing on the suggested schedule, the stock system works great.
And the only modification I made to my primary is that now it is vented. The 1965 - e1966 aluminum primary units for Big twin medals was non-vented which led to leaks. HD fixed the problems with a vented primary and sold a retro-fit kit for the early models
My 66 was isolated, my 82 is, my 72 is and of course my TWINKIE is. I agree its not a disaster to leave it in the system but if it was such a brilliant idea they wouldn't have gone to an isolated setup over time. The isolated setup also allows you to run a different product in the primary, if you so desire and you can tell what's leaking in an instant by the color, not to mention the other benefits.
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