慢慢来。
Take your time.
It consists of an adjective and verb.
Since 慢慢 is an adjective but used in an adverbal way, I assume that this one below should be the original form of 慢慢来.
慢慢 + 地 + 来。
I tried googling with that, and found it used many times. (not as many though)
So are 慢慢来 and 慢慢地来 the same?
Syntactically they are the same. 地 following adverb can be omitted in spoken language and in many cases, written language too. In ordinary cases, the omission does not change the meaning or the tone of the phrase.
In your example, however, the meanings are different. As the other answer suggested, 慢慢地来 is just an ordinary phrase meaning come slowly; proceed slowly, mostly used in narratives, e.g.
他慢慢地来了。He came slowly.
Note the above example sounds lack a point. In real life usage, it is more natural to specify the action verb, e.g.
老人扶着拐杖，慢慢(地)走过来了。Supporting himself with a cane, the old man was slowly coming over.
On the other hand, 慢慢来 is always used for its metaphorical meaning take your time; take it easy. It's mostly used as an imperative instead of narrative:
没关系，慢慢来。Don't worry, take your time.
慢慢来，小心点。Take it slowly and be careful! (as when someone is moving an antique for you)
There is a situation where 慢慢来 is used in a narrative sentence and interchangeable with 慢慢地来. They are used as adjective or adverbial phrase as opposed to predicative phrase. Note how the following examples are narratives from 3rd person view, although you can use them to make suggestions to the listener just like using imperative sentences.
感情的事要慢慢(地)来。Love cannot be forced.
这种类型的工作要慢慢(地)来。This kind of job takes time and patience.
Not really, 慢慢来 is much more used in speaking Chinese.
Like:
慢慢来, you can do it well, finally.
If you see 慢慢地来, the 慢慢地 is a adv. of v.(来), so you can only use it when you speak to someone who 来 meet you.(It can also be instead by 慢慢来)
