I'd just put pure R135a. When I had the same issue on my e46, I just filled it up with a can from Walmart, and kept driving it for another 30,000+ miles before I sold it. It was still blowing ice cold.

If you suspect you have a leak, then use a dye while you're filling it up, and monitor the A/C lines on a regular basis. Then properly fix the leak if there are any. At least, that's what I'd do.

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