Re: Splicing Old Double Braid Line--Sewn Splice?
If you have done this with old line and it failed away from the splice, I really think that (1) your sewed splice is actually pretty strong, but (2) you probably ought to reconsider and get new line. That's just me. I just yesterday gave away three shrimp baskets full of old sheets and halyards and preventers and thises and thatses in addition to several years worth of mooring lines replaced. So obviously I am biased towards new line so take that with a gram of salt. But in your situation I have sometimes spliced both sheets permanently into the clew with an ordinary double braid eye splice so there is nothing at all to hang up when pulling a headsail in tight between the shrouds. This would be a little awkward when racing because you have to run the new sheets through their blocks when changing sails but I don't race. If it is a short run I leave the dock with the sails I am going to come back in with, and jiffy reef the main and roller reef the jib if needed. But if you need detachable sheets for speedy changes then I guess you are stuck with the soft shackles.
If you identify an area prone to chafe, it is good to sew on another layer of cover, though. I have done that. Just slide it on and stitch it to the original cover and whip the ends. Prolongs sheet life, yeah. There's a very useful outlet to your needle skills.
On ships I have spliced old 12" Samson double braid mooring lines and yeah it takes all day but it can be done. The fresh water and detergent thing gets funny looks but it definitely helps. With patience and making sure that the cover and core slide freely, your old halyard can be spliced conventionally. A hard strain to reduce the splice diameter will help it to bury but if it doesn't fully bury, it still has a pretty good amount of strength. Sometimes you have to take tension and release it through a few cycles to get the crossover down to a compact size. Smacking it a few dozen licks between two hammers helps. Any lumps or protuberences will hang up when you go for the bury. I will even cut an offending yarn or three if necessary. So don't be shy about splicing old stuff. And I hope you will reconsider buying new stuff. And nothing wrong, it appears, with your sewed splice if the stitching doesn't catch any chafe and fail on you. And good luck. Have a happy project!