E34 525tds only starts with start up spray

So had a flat battery a few wks ago nd couldn't get it to start no matter how long I jumped it for. Friend of mine recommended using some start up spray nd it started after turning over the engine for about 5 seconds. Went to start it dis mornin nd same thing wouldn't start until I used the start up spray. Also notice that I've a slight diesel leak from the pump in the front of the engine nd I know the 1 in the fuel tank is f##ked but that never bothered me as I've always kept it above quarter way tis 3 quarters full at the moment. Question is if I changed the seals in the front pump and pump in the fuel tank would it sort dis issue. Money is tight at the moment nd I dont wanna be throwing good money after bad as the sill are in a bad way on it too nd once nct is up in May I'll b scraping the body nd selling the oily bits to a friend of mine for an e30 project. Anyone recommended anything else I'm far from a mechanic but well able to get stuck in and all advice welcome