Bongo Fury

I recently changed the double filament bulb on a lighting board, which I presume would be the same as the rear lights on the Bongo. The replacement only lasted a very short while. Investigating the bulbs further I found this:

Original bulb SE 12v - P21/5W P21/5 (E19) 2K2
Replacement bulb that blew AIA 12v - 21/5W P21/5 (E4) 2E1.

The contacts on the base were slightly different with the original having a 'spot' on the rim between the two contacts.

I think the proprietor of the car accessory shop thought I was a twit. Does anyone know the difference and is there a lesson here about bulbs for the bongo?

It's all down to cost (not always to your benefit)
There are many cheap (and nasty) bulbs being manufactured around the world.
Stick to a named brand and they should last, (I have had many calls in my life as an electrician,by people convinced there is something wrong with their wiring in the house as their bulbs are blowing
Turned out every time they were using the cheap ones from their local DIY store.
You can't always tell just by price, as many outlets buy in the cr*p but sell at quality prices.
Moral: buy from Halfords or the like, if it then blows quickly, take it back for a replacement.