OK. My advice is this:
1.Find a shop/parts distributor that specifically deals with Volvo Marine stuff. They will have the best knowledge and resources for parts.
2.Try to get a "service manual" for your engine (from a dealer, parts shop, online, etc). Hopefully it's available - it will explain the fuel system and "bleeding" procedure for your engine.
3. Learn to change fuel filters. Often there are two. If there are two (trace the fuel line from tank to injector pump), the first one (from tank), named "primary", is probably not a Volvo part. It would be in a filter housing mounted off the engine (usually). If there is a primary (two fuel filt system) the housing brand/part num, or element id, is what you need to find the part. There will be a fuel filter mounted on the engine. Note the brand and PN. Probably, there are many brands that will fit. My opininion - get them from the Volvo guy.
4. Carry extra fuel filters.
About fuel and diesels:
crap in the fuel is a common issue with diesel and diesel engines (long story) that stop the engine. Long story, I'll leave it at that. It's a basic fix, if you can swing a wrench and get dirty. Also, unlike gas engines, diesels can't deal with any air in the fuel system.
Anyway, in my experience, being able to change fuel filters, and bleed the air from fuel lines, has saved the day several times.
Also, look into "Biocides" (Biobor is wellknown) that kill the crap growing in your fuel tank.
Changing oil as recommended by the manufacturer is important. More important than with a gas car. Old engines - more often. Another long story. Again- the interval will be speced in the manual. I'd guess 100 hrs, or annually? Important.
Oil change. Get old oil out. Remove filt. Replace filt. Replace oil. Check level ( not over high mark). Run engine a few minutes (watch oil pressure gauge, should go up in 5-10sec). Shut down, check oil level after a few minutes. Add oil to bring level near high mark (not over).
Getting oil out: unlike a car, usually pulling the plug from the oil pan is not an option. Marine places sell hand pumps for $40 (give or take) are made for this. One way is to suck oil out the dipstick tube. Works good if the oil is warm.
Filters are usually spin on. Spin the old one off, spin the new one on. Problem is, often they are very hard to get at ( and other issues with tight installations).
Oh ya. Get a bunch of "Sorbent" pads. They absorb oil that is trying to get in your bilge.
oil change: 1st time: 4 hrs. Including research, buying parts, figuring it all out, dispossing of crap, washing hands. 2nd time: 45 min
fuel filts: 1st time 4 hrs. 2nd time: 30 min.
That 1st 8 hrs includes learning how to do it. For someone new to it all. I wonder if that's what the "Marine Mechanic" was thinkin?
Let me know how it goes
oh ya. The "DE" ( or any service starting with D) is obsolete. It's all changed. Ask a Volvo guy.