I run DOT 4 and change it every two years regardless of mileage — that's BMW's fixed interval. It matters because brake fluid's hygroscopic: the water it absorbs drops the boiling point and gives you a spongy pedal or fade under hard use.
Never use DOT 5 (silicone) in an E36.
I bleed until clean fluid runs from each nipple, working from the corner furthest from the master cylinder inward.
For a flush you'll want fresh DOT 4 — I've put
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