I did my plugs at 94k and the boots were in great shape. Plugs had never been done. on a Coil on plug application like we have I've had good results with putting di-electric grease on the boots; inside and out. Nice coating all over the outside and put a small squirt into the boot for it going on the plug. Next time it's much easier and it keeps moisture out. Extends the life of the boot tremendously too. Just my 2 cents.
As for plugs. You have 3 to choose from the way I see it.
1- OE NGK plugs (What I did due to they will last a 100k interval, are OE and cheapest option of the list)
2- Irdium NGK .6mm tip Will last about 40-60k
3- Iridium Denso .4mm tip Will last about 40-60K
I steer clear of the Bosch +'s. Never had good results. Nor have I seen them come as OE. If I use a Bosch, it's the OEM Bosch. Like in my 335i. Very odd plug. Stuck with the OE bosch. I wanted to use a OE Irdium NGK, but they don't make that plug for our car. That would be sweet if they did. That's probably my favorite plug. 100K life and iridium. And it DOES come as an OE plug in a ton of cars. even the corollas have them OE, Lexus, ETC. One of the best overall plugs you can buy IMO. Not sure why they don't have a listing for it on the 530i.
DD: 2003 530i 5spd manual sport package. Conti DWS's, Llumar ATR, White LED lighting. TLC on-going.
Garage queen: '07 335i Sedan, base pkg, 6spd Manual, Procede 3 V5 w/NLS, staggered 18" 313's w/Conti DWS's, OS Giken TCD LSD, VAC Street Diff Cover, Akebono Euro Pads, CDV Removed, Black BMW Grilles, Interior & Exterior white LED lighting, LUX Angel Eyes, Debadged, Llumar ATR Tint.
Last edited by FLE39; 12-07-2012 at 08:42 PM.