Oil cooler lines, replace ?
 

It can't hurt to replace them and their corresponding crush washers. However, I personally do not replace mine until I see signs of degradation. The oil cooler lines hold up for a long time. I've never personally had one completely fail. I've had a few start to get damp and I replaced the sets right away. The original oil cooler lines are quite expensive. In the neighborhood of about $400 for both lines from Mazda.

If you've already cleaned them up really good, and after driving for a bit there's zero evidence of any oil seepage/dampness/weeping anywhere, just leave them be. Like the other guy said, they last a long time and they rarely fail catastrophically by busting open - more likely the crimped on hose fitting loosens up, and oil starts seeping out.

As for replacement lines, Racing Beat, Mazdatrix and a few others sell SS braided line sets to replace the stock lines for less than what you'll pay for the OEM Mazda parts.

Back in 2015 while driving the '89 TII, the oil alarm went off, first time since I purchased new, pulled over and a stream of oil on the ground.
Had it flat-bedded home, oil cooling line burst and replaced both with OEM lines-$350.

If they're leaking, replace them. If not, let it be.

My car's original lines were fine and dandy at 99k when I began the 20B conversion. The bulk of the cost in converting to -10AN lines is in the adapters, mainly the special 90 degree one to clear the frame rail at the oil cooler. This is the route the Mazdatrix kit goes. Personally, $50 for an adapter fitting seems like a big investment when one could just move the oil cooler over about 1" with some simple flat brackets. That would create enough clearance to use a generic adapter and 90 degree hose end. Another option is a 18mm to -10AN banjo adapter. A quick check on ebay found them for $15-25. Shops like Jegs or Summit Racing would probably be similar in price.

As for hoses, any -10AN hose will do just fine. I have Jegs Push-loc hose on my car since it was easy to work with and relatively cheap. Aaron Cake used a similar type of hose on the Cosmo.

Where was the burst point? I would bet it was at one of the hose crimp joints rather than somewhere in the middle of a line. Usually the crimp fittings start weeping a bit before they fail catastrophically. Easy to miss the warning signs though, especially for the fittings closest to the oil cooler, where they are more difficult to clean & visually inspect periodically.

I have the Rotary performance ones on my car. They are SS braided but have fitting like the stock ones. Had them 15 years or so with no problems.

https://www.rx7.com/store/rx7/fcoilcoolerlines.html

I also have the Rotary Performance braided SS lines on my 90 GXL. Have had them for about 16 years with no problems.

Actually it burst under the protective covering away from the fittings, but it was actually seeping for about 13 years before it burst. Sounds like a long time, but when the remanufactured engine was installed back in 2002, I believe they did some damage to the cooling line as there was no evidence of seepage before the engine change. Never any oil on the ground, but one could see wetness for years, but the car only used maybe 2k miles per year.

I do agree that if the seeping were investigated after first sighting, the hoses would have been replaced preventing the problem.

Nice job pulling over in time when the oil level warning light came on. That could have gotten really ugly really quick.

When I blew my motor I took advantage of the situation and replaced the lines with Racing Beat SS oil cooler lines. Oil and cooling are imperative for rotaries, I wanted piece of mind.
RB Oil Cooler Lines