As has been said - wet and dry.
For those, I'd take some *QUALITY* wet and dry at about 1000, soak it for 20 mins, then using a hard, flat block about 2x1" start rubbing very gently. You'll see the paint start to dull, and you should only be touching the raised sections. You have to use a block; using your hands will not get it flat.
Once the worst of the build-up has gone, switch to 2000 to finish and get it flat. again, you should barely be making a mark on the original paint until it's almost perfectly flat.
Then use a bit of cutting compound to finish.
Again, loverly frame & fork.