Slow crankin starter

1995 xj6 with 100k pampered miles,,regular oil changes etc....occasionally will start then stall,,upon trying to start again it cranks slow as if the battery is dying,,then starts after a fewe attempts,,I noticed teh firewall battery connection needed the nylon spacers replaced which I did and retightened,,it has happend twice again in three weeks,,any Ideas??

Thanks

Sounds like the timing might be off. Or if it runs untill warmed up and then dies, the timing might not be advancing properly.