I have a 94 with a 318 and I have to charge it up every summer. I assume it has a slow leak and the price of 2 cans is a lot cheaper than trying to trace down a leak. I've been doing this for about the last 5 years.

 

Sequential is multi-port but with a twist. Many Multi-port's fire the left bank all at the same time and the right bank all at the same time. Sequential means the each cylinders injector fires just before the intake valve opens.
Gives a little better hp and economy over Multi-port injected.

Throttle Body Injected has 1 or 2 injectors on top of the "carburetor" unit.
Sequential and Multi-Port's have individual injectors in the intake manifold just above the cylinders intake port.

 

So $30/year in R134a times 5 years ($150 so far) is cheaper than an el cheapo $12.00 UV detection light and glasses, plus another $5 for a 1.7 oz. pressurized can of UV dye?