As far as seals go, you're guaranteed with an Iwata, they use Teflon needle packing, (the seal behind the air supply and trigger), though most cheapies use them now.
The problem one on the cheapies is the 'O' ring at the nozzle, the Iwata uses a different setup altogether and doesn't have an 'O' ring at the nozzle, (I'm pretty sure of that anyway, correct me if i'm wrong folks using Iwata's), some other expensive brands use teflon seals at the needle.
As Graham says, the real bonus is that you'll always be able to get spare parts for the Iwata.
The problem one on the cheapies is the 'O' ring at the nozzle, the Iwata uses a different setup altogether and doesn't have an 'O' ring at the nozzle, (I'm pretty sure of that anyway, correct me if i'm wrong folks using Iwata's), some other expensive brands use teflon seals at the needle.
As Graham says, the real bonus is that you'll always be able to get spare parts for the Iwata.
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