Need HELP!!

I have a 98 S70 T5, it seems so hard to start the engine (it cranks maybe more than 5 mins to start). It's fine when the engine is hot, but after awhile(after the engine cool down for half hour, it's hard to start again) So I brought it to the mechanic shop and do the diagnostic test and there were 3 P-codes came out, which are: P0172 P0410 P0455 Can anyone explain to me what are they about? I really have no idea. Also, there is another problem, oil leak from the oil return line, which is leaking from the engine block, as I know, it should be the problem for the seal. But after it had been replaced, it seems worst than before......... Please give me some advices. I really love this car, so I want to fix it and keep it for long term.

oil leak 

cant help much with codes, but try looking up in a haynes manual, i think they are listed there. 2 regarding oil leak, sounds like the green seal youve fitted in the oil return pipe may of got twisted. get a new one, and when fitting, smear the seal with petrolium jelly (vaseline) this helps it slide in and prevents twisting. hope that helps, it did with mine