RUSTY.
As above, Sikaflex is so much stronger and easier. I've done two Mini's this way. I've used SikaFlex on Cars, Buses. Trams and Trains. It's great stuff!
The only issue is that the seam moulding is stuck for life. To remove it, requires grinding down the fold of the moulding, then peeling it off as two bits. However, mouldings are cheap, and if you do it right from start, they can stay on for near eternity.
My process:
Clean the seam back to clean raw metal.
Couple coats of primer
Fill new seam moulding with Sikaflex
Clamp onto seam. (G clamps, lengths of wood, etc etc)
Gently wipe excess away. Avoid using solvents (at this stage)
Leave overnight.
Next day (or at least (say) 8-10 hrs later, remove clamps and any wedges of wood etc.
The overfill (Ooozz) can simply be scrapped off using your finger nails (no good for nail chewers!)
You should be able to get all visable Sikaflex off, right up to the join.
You can now sand (240grit) lightly, than apply another light coat of primer.
Nothing looks worse than tracks of sealer down each side. All sealers flex and shrink and crack the paint and allow for rust. The above method makes it totally waterproof.
One of mine:

Goodluck.
Alex.