The "goop" is Tamiya extra thin cement mixed with sprue to form a very thick plastic filler that has the same consistency as the plastic of the kit. Once it is dry it can easily be sanded and does not shrink. I've found it the best solution to filling gaps for my needs. Though we modellers all have our preferred methods of doing things.
I have a post on Britmodeller about this here:
Also during the test fit I realised that parts C45 (the engine fan) & D24 would not be seen at all so there was absolutely no point in painting it. Same goes for the fitting of the photoecth part PE27. You're never going to see it so there is really no point fitting it.
With the engine exhaust parts (C7 & C55) filled and dry it was ready to sand.
I rolled up a piece of wet & dry sand paper and rotated it whilst pushing it in and out. After about 15 minutes of that it was done.
Now, to re-paint it!....................