Three general "maintenance" and "dealing with mechanics" questions

[trinacriabob]

Three questions:

1)  With cars now having platinum and iridium spark plugs, the intervals between changing them has become fairly long.  I'd finally like to change my original platinum spark plugs.  Are there ever issues where the spark plugs have been in the cylinder block for so long that its tough for the mechanic to get them out?  Is there something they can do prior to putting on the socket wrench that will make them turn more easily?  Also, do you know if, on transversely mounted GM V-6 engines, they access the 3 rear spark plugs by the firewall (a) from above or (b) by hoisting up the car and working from the space behind the exhaust manifold but in front of the catalytic converter?

2)  What might cause a engine to shudder slightly when the ignition is turned on?  It doesn't happen all the time.  Most of the time, the engine remains still and you just hear it turn over.  In a RWD car that my dad once had, the engine did this upon ignition or during hard acceleration because a motor mount was giving up the ghost, largely because of oil that was on the underside of the chassis.  Any ideas when this is NOT the case?

3)  Are independent mechanics amenable to ordering parts from Amazon?  Amazon has more auto parts than do some of the big retail chain auto stores, along with reviews of the parts, and the prices are often favorable.  I know that the mechanic would have to mark them up.  Have you known of independent mechanics that will order from Amazon or do they just tend to stick to brick and mortar stores that can deliver auto parts to them?

Let me know what you think.  Thanks.

[balthazar]

1. They can spray penetrant on the plugs if they're really tight in there. Kroil is among the best on the market.

3. I don't see a garage willing to wait 24 hrs min for an Amazon package when their business model is 'turn & burn' as far as getting vehicles in & out the door. The longer a vehicle sits in a service bay the less invoices they write. But you need to ask them your question.

[trinacriabob]

10 hours ago, balthazar said:

3. I don't see a garage willing to wait 24 hrs min for an Amazon package when their business model is 'turn & burn' as far as getting vehicles in & out the door. The longer a vehicle sits in a service bay the less invoices they write. But you need to ask them your question.

What I meant is if the part is pre-ordered.  When I had my ISS replaced several months ago and I wanted a GM part, the service appointment was made in advance.  The part, obtained from a dealership, apparently, was already there.  I'm wondering if some mechanics have Amazon accounts.

[Robert Hall]

Anecdotally, I know my local independent repair shop ordered an alternator for my sister's Cadillac from Amazon when it was in the shop a couple months ago, they said it was cheaper and faster than sourcing it other ways. 

[trinacriabob]

2 hours ago, Robert Hall said:

Anecdotally, I know my local independent repair shop ordered an alternator for my sister's Cadillac from Amazon when it was in the shop a couple months ago, they said it was cheaper and faster than sourcing it other ways. 

Okay, good, it's something that some mechanics will do.  It's not unheard of.  And I'm guessing this part is performing as it should.

[Cmicasa the Great]

Dealerships are within a network of other dealers. The part can also be obtained from another dealership.